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Bull. Soc. Chim. Belg. vol. 106 / n° 9-10 /199 7 EUROPEAN SECTION

0037-9646 / 97 / $ 2.00 + 0.00 © 1997 Comite van Beheer van het Bulletin v.z.v

UNEXPECTED RING OPENING OF OXAZOLO[3,2-a]PYRIDINIUM CATION IN REACTION WITH MeONa. CRYSTAL STRUCTURE OF 2-PHENYLOXAZOLO[3,2-a]PYRIDINIUM PERCHLORATE AND l-[l,l-DIMETHOXY-l-PHENYLETHYL-2]-2-PYRIDONE Eugene V. Babaev,* Svetlana V. Bozhenko, Dmitriy A. Maiboroda, Victor B. Rybakov and Sergey G. Zhukov Chemistry Department, Moscow State University, 119899 Moscow, RUSSIA Dedicated to the late Professor Gerrit L 'abbe

ABSTRAC T Selectivity of ring opening reactions of the oxazolo[3,2-a]pyridinium cation in reactions with nucleophiles (cleavage of either C5-N bond or C 8a - 0 bond) is reviewed, and the novel direction of ring opening (cleavage of C2-O) bond is discovered. 2-Phenyloxazolo[3,2-a]pyridinium perchlorate in reaction with MeONa is transformed t o l-[l,l-dimethoxy-l-phenylethyl-2 ] -2-pyridone. Crystal structures of the final ketal and the starting material are reported, and the clear alternation of length of C-C bonds in both molecules is observed. Keywords : Oxazolo[3,2-a]pyridinium perchlorate, ambident properties, ring opening, synthesis of ketals, 1 -[ 1,1 -dimethoxyethyl-1 -phenyl-2]pyridone-2.

INTRODUCTIO N The structure and reactivity of the aromatic system of oxazolo[3,2-a]pyridinium cation I (first obtained long ago [1]) is still poorly investigated. There may be few resonance structures (Ia-c, Scheme 1) for the cation I, and it Scheme 1.

is still unclear whether the 6-membered ring follows a delocalized pattern (as in the pyridinium salts) or the double bonds ar e localized (as in the pyridone-2). There are still no experimental data on the geometry of this cation.

Another specific problem is related to the reactivity of the cation I toward nucleophiles. As it was considered for a long time, the nucleophiles may attack only the bridgehead carbon atom C8a, causing ring opening of the oxazole fragment. Thus , in reaction with alkali [2], primary amines [3], some P - and As-nucleophiles [4], sodium hydrosulfide [5], and carbanions [6,7] only the cleavage of 5-membered ring of bicycle I was observed, and the products may undergo further

recyclizations, Scheme 2,A. However, a s we proved very recently [8], the action of secondary amines causes cleavage of the pyridinium fragment of the cation I, Scheme 2, B . Finally, in the reaction of the cation I with NH 3 [5] (namely, if liquid ammonia was used as the reaction media) the mixture of tw o products was obtained (Scheme 2 , C) , confirming that both possibilities of 5- and 6-membered rings cleavage can be realized

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Scheme 2.

Overview of known ring opening reactions for derivatives of the cation I.

simultaneously. Therefore, the cation I should be regarded a s an ambident system toward nucleophilic attack with the possibility of cleavage either of the C 8a - 0 bond (opening of the oxazolium fragment) or the C5-N4 bond (opening of the pyridinium fragment). Both bonds broken in this reaction are adjacent t o either of tw o bridgehead atoms, C8a or N. In the present communication we discover the third, quite unexpected, possibility of ring opening for the cation I, namely the example of cleavage of the C2-O bond (that is not adjacent t o a bridgehead atom). W e also report the crystal structures of the product and of the starting material -- 2-phenyloxazolo[3,2-a]pyridinium perchlorate. RESUL T AN D DISCUSSIO N Scheme 3 .

W e found that 2-phenyloxazolo[3,2-a]pyridinium perchlorate (II) in reaction with MeON a in methanol is almost quantitatively transformed t o 1[l,l-dimethoxy-l-phenylethyl-2]pyridone-2 (III), Scheme 3 . Mass spectral and elemental analysis dat a for the product III confirm its molecular formula t o b e a formal adduct of tw o MeO-groups t o the cation II. In the 1H and 13C NM R spectra the signals in the aromatic region correspond t o the fragments of pyridone-2 and phenyl group, and the signals of tw o equivalent methoxy groups and of CH2-group appear in the region expected for ketals. The result should be regarded a s the first example of cleavage of the C 2 - 0 bond in the cation I

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(possible intermediates are shown in brackets in Scheme 3). The hypothesis that ring opening occurs via an alternative way should be rejected. Thus , if one assumes that the initial nucleophilic attack occurs a t the bridgehead position C8a, the intermediate formation of l-phenacyl-pyridone-2 (IV) would be expected. (Dealkylation of N-alkyl-2methoxypyridinium salts t o N-alkylpyridones-2 is well known [1].) However, even after prolonged keeping in the reaction conditions (MeONa/MeOH) the pyridone I V wa s not transformed t o th e ketal III. In order t o understand the abnormal direction of cleavage of the C2-O bond in the cation II we performed semiempirical quantum-chemical MND O calculations of the isomeric intermediates of ring opening. The energy o f isomeric adducts Va c (between cation II and MeO-anion) and possible isomeric products of ring cleavage Vla- c are presented in Scheme 4. As it is evident, the formation of the C5 adduct V a is the most favorable from thermodynamical viewpoint. (By contrast, the zwitter-ionic intermediate V c has the highest energy.) However, the process of the nucleophilic addition may be reversible. In turn , the cleavage of

the C2-O bond results in the most stable product of reaction VIc, that is the evident precursor of the experimentally observed ketal III. Therefore, the experimentally observed ring opening (II t o III involving intermediate Vic) may be treated in terms of the thermodynamically controlled reaction, whereas in the other ring opening reactions (Scheme 2) the kinetic control may play a n important role, X-ray data completely confirm the ketal structure assigned t o the product III. In Schemes 5,6 the crystal structures of the starting material II and the product III are presented. The observed geometry of the molecule II provides a clear answer t o the question, which of resonance structures (Ia-c) would better represent the structure of the cation I. With evidence, there is pronounced alternation of bonds ' length along the six-membered fragment in the structure II, so that it closely resembles a butadiene-like pattern in the pyridone III (cf. Tables 1 -- 4) . Therefore, the contribution of the structure Ic may be neglected, and the geometry of the cation I would be better regarded a s the superimposition of the oxazolium ring and butadiene fragment (contribution of the structures l a and Ib) .

Scheme 4 .

Energy (MNDO , kcal/mol) of the isomeric adducts Va-c of the cation II and MeO-anion and of the ring opening products Vla-c . The most stable intermediates are Va and VIc.

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Scheme 5. View of the molecule II and atom numbering [10]

Scheme 6. View of the molecule III and atom numbering [10].

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Table 1. Structure of the molecule II. Atomic coordinates (*104) and equivalent temperature factors Ueq (A2*103) defined a s one third of the trace of the orthogonalized Uy tensor.
Atom Cl(l) Cl(2) O(ll ) O(12) O(13) O(14) O(21) O(22)
CX23) X Y Z
Ueq

Bond lengths [A] and angles [deg].

O(24) C(1A) C(1B) C(2A) C(2B) O(3A) O(3B) C(4A) C(4B) C(5A) C(5B) C(6A) C(6B) C(7A) C(7B) C(8A) C(8B) N(9A) N(9B) C(10A) C(10B) C(11A) C(11B) C(12A) C(12B) C(13A) C(13B) C(14A) C(14B) C(15A) C(15B) H(1A) H(1B) H(5A) H(5B) H(6A) H(6B) H(7A) H(7B) H(8A) H(8B) H(11A) H(11B) H(12A) H(12B) H(13A) H(13B) H(14A) H(14B) H(15A) H(15B)

3939(2) 8872(2) 2177(7) 3406(7) 4057(6) 6158(6) 6392(7) 9319(7) 9613(8) 9890(10) 9410(8) 3912(9) 8569(7) 5269(7) 6456(5) 7169(5) 6069(8) 6878(8) 4232(9) 8270(11) 4307(10) 7520(13) 6124(10) 5465(12) 7921(10) 4163(11) 7846(6) 4894(6) 9346(7) 5168(8) 11540(8) 7018(9) 12257(9) 6901(10) 10833(9) 4958(11) 8691(10) 3080(10) 7953(9) 3193(9) 684(80) 2724(80) 3049(72) 9452(85) 3189(84) 8250(116) 6178(80) 5038(74) 9211(92) 7120(79) 2372(84) 8193(78) 13738(84) 11910(70) 11280(68) 4832(83) 7837(80) 1716(84) 6627(69) 2038(81)

514(1) 5607(1) 1121(3) -511(3) 801(3) 647(3) 5668(3) 5900(3) 4603(3) 6270(4) 2081(3) -2962(4) 2101(3) -2947(3) 2669(2) -2366(2) 2986(3) -2027(3) 3580(3) -1405(4) 3797(4) -1174(5) 3456(4) -1535(4) 2883(4) -2129(4) 2647(2) -2377(3) 1662(3) -3401(3) 1157(3) -3359(4) 704(3) -3827(4) 748(3) -4330(4) 1243(4) -4370(4) 1701(3) -3905(3) 1734(33) -3220(33) 3772(29). -1163(35) 4216(34) -768(48) 3677(33) -1338(31) 2629(38) 2422(33) 1129(34) -3000(32) 348(34) 3792(28) 448(29) -4609(34) 1295(33) -4715(34) 2021(28) -3931(33)

3020(1) 3208(1) 3677(2) 2744(3) 2280(2) 3348(2) 3431(3) 2479(3) 2933(3) 3911(3) 2403(3) 2251(3) 1697(3) 1559(3) 1964(2) 1850(2) 2842(3) 2730(3) 3405(3) 3313(4) 4273(3) 4179(4) 4580(4) 4449(4) 4007(3) 3863(4) 3131(2) 2996(2) 764(3) 617(3) 462(3) 21(3) -416(3) -868(3) -1015(3) -1160(4) -735(3) -580(4) 153(3) 308(3) 2450(28) 2306(29) 3150(25) 3084(30) 4700(31) 4523(42) 5173(31) 5031(30) 4150(32) 5998(28) 882(31) 216(28) -608(29) 1256(26) -1570(27) -1671(30) -1107(30) -801(30) 328(24) 699(29)

42(1) 50(1) 92(2) 77(1) 63(1) 64(1) 84(1) 86(1) 104(2) 131(2) 37(1) 42(1) 32(1) 36(1) 38(1) 42(1) 37(1) 39(1) 46(1) 56(2) 52(1) 67(2) 54(1) 65(2) 47(1) 57(2) 36(1) 39(1) 31(1) 35(1) 39(1) 42(1) 44(1) 49(1) 44(1) 53(2) 44(1) 49(1) 39(1) 44(1) 52(14) 43(15) 33(12) 51(16) 56(15) 102(25) 52(14) 41(13) 70(18) 43(14) 57(16) 43(14) 57(15) 30(11) 29(11) 48(16) 48(15) 55(15) 21(11) 48(15)

Cl(l)-O(12) C1(1>O(11) Cl(l)-O(14) C1(1>O(13) C1(2>O(24) Cl(2)-O(23) C1(2>O(22) Cl(2)-O(21) C(1A>C(2A) C(1A)-N(9A) C(1B)-C(2B) C(1B>N(9B) C(1B)-H(1B) C(2A>O(3A) C(2A>C(10A) C(2B>O(3B) C(2B)-C(10B) O(3A)-C(4A) O(3B>C(4B) C(4A>N(9A) C(4A)-C(5A) C(4B)-N(9B) C(4B)-C(5B) C(5A)-C(6A) C(5A)-H(5A) C(5B)-C(6B) C(5B)-H(5B) C(6A)-C(7A) C(6A)-H(6A) C(6B)-C(7B) C(6B)-H(6B) C(7A>C(8A) C(7A)-H(7A) C(7B)-C(8B) C(7B)-H(7B) C(8A)-N(9A) C(8A)-H(8A) C(8B)-N(9B) C(10A)-C(15A) C(10A)-C(llA) C(10B)-C(llB) C(10B>C(15B) C(11A>C(12A) C(11B>C(12B) C(11B>H(11B) C(12A>C(13A) C(12A>H(12A) C(12B)-C(13B) C(13A)-C(14A) C(13A)-H(13A) C(13B)-C(14B) C(13B>H(13B) C(14A)-C(15A) C(14A)-H(14A) C(14B)-C(15B) C(14B>H(14B) C(15A)-H(15A) C(15B>H(15B) O(12)-C1(1)-O(11) O(12)-C1(1)-O(14) O(11)-C1(1)-O(14)

1.418(4) 1.418(4) 1.431(3) 1.433(3) 1.386(4) 1.397(4) 1.426(4) 1.428(4) 1.330(6) 1.392(5) 1.319(6) 1.387(6) 0.79(4) 1.399(5) 1.445(6) 1.393(5) 1.455(6) 1.340(5) 1.341(5) 1.348(5) 1.378(6) 1.344(5) 1.377(7) 1.357(7) 0.94(4) 1.362(8) 0.88(5) 1.386(7) 0.92(5) 1.388(9) 0.80(6) 1.356(7) 0.92(5) 1.331(8) 0.90(4) 1.367(6) 0.92(5) 1.357(6) 1.382(6) 1.402(6) 1.385(6) 1.389(6) 1.362(6) 1.377(7) 0.87(4) 1.379(7) 0.95(5) 1.367(7) 1.369(7) 0.86(4) 1.379(7) 0.80(4) 1.379(6) 0.86(4) 1.375(7) 0.96(5) 0.86(4) 0.89(4) 110.6(3) 109.0(2) 110.4(2) 108.9(2) 108.7(2) 109.3(2)

Table 2. Structure of the molecule II.

O(12>CK1HX13) O(11)-C1(1)-O(13)

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O(24)-C1(2)-O(23) O(24)-C1(2)-O(22) O(23)-C1(2)-O(22) O(24)-C1(2)-O(21) O(23)-C1(2)-O(21) O(22)-C1(2)-O(21) C(2A)-C(1A)-N(9A) C(2B)-C(1B>N(9B) C(2B)-C(1B>H(1B) N(9B)-C(1B)-H(1B) C(1A)-C(2A>O(3A) C(1A)-C(2A>C(1OA) O(3A)-C(2A>C(10A) C(1B>C(2B)-O(3B) C(1B>C(2B)-C(1OB) O(3B)-C(2B)-C(10B) C(4A)-O(3A>C(2A) C(4B)-O(3B)-C(2B) O(3A>C(4A)-N(9A) O(3A)-C(4A)-C(5A) N(9A>C(4A)-C(5A) O(3B)-C(4B)-N(9B) O(3B)-C(4B)-C(5B) N(9B)-C(4B)-C(5B) C(6A>C(5A)-C(4A) C(6A)-C(5A)-H(5A) C(4A)-C(5A)-H(5A) C(6B)-C(5B>C(4B) C(6B)-C(5B)-H(5B) C(4B)-C(5B>H(5B) C(5A)-C(6A)-C(7A) C(5A>C(6A)-H(6A) C(7A)-C(6A>H(6A) C(5B)-C(6B)-C(7B) C(5B)-C(6B)-H(6B) C(7B)-C(6B)-H(6B) C(8A)-C(7A)-C(6A) C(8A)-C(7A)-H(7A) C(6A)-C(7A)-H(7A) C(8B)-C(7B)-C(6B) C(8B)-C(7B)-H(7B) C(6B)-C(7B)-H(7B) C(7A)-C(8A)-N(9A) C(7A)-C(8A)-H(8A) N(9A)-C(8A)-H(8A) C(7B)-C(8B)-N(9B) C(4A)-N(9A)-C(8A) C(4A>N(9A)-C(1A) C(8A>N(9A)-C(1A) C(4B)-N(9B)-C(8B) C(4B)-N(9B)-C(1B) C(8B)-N(9B)-C(1B) C(15A)-C(1OA)-C(11A) C(15A)-C(10A)-C(2A) C(11A)-C(1OA)-C(2A) C(11B)-C(1OB)-C(15B) C(11B)-C(1OB>C(2B) C(15B)-C(10B)-C(2B) C(12A)-C(11A)-C(1OA) C(12B)-C(11B)-C(1OB) C(12B)-C(11B)-H(11B) C(1OB)-C(11B)-H(11B) C(11A)-C(12A)-C(13A) C(11A)-C(12A)-H(12A) C(13A>C(12A)-H(12A) C(13B)-C(12B)-C(11B) C(14A)-C(13A)-C(12A) C(14A)-C(13A)-H(13A) C(12A)-C(13A)-H(13A) C(12B)-C(13B)-C(14B) C(12B)-C(13B)-H(13B)

115.4(4) 109.2(3) 108.3(3) 109.5(3) 107.6(3) 106.6(3) 107.1(4) 107.9(4) 133(3) 119(3) 108.8(4) 134.0(4) 117.2(4) 108.4(4) 133.8(4) 117.7(4) 107.0(3) 107.0(3) 109.1(4) 128.5(4) 122.4(4) 109.1(4) 128.6(5) 122.3(5) 115.8(5) 127(3) 117(3) 115.6(6) 128(3) 116(3) 122.5(5) 122(3) 116(3) 121.7(6) 116(5) 122(5) 120.1(5) 120(3) 119(3) 120.6(6) 122(3) 117(3) 117.9(5) 126(3) 116(3) 118.5(6) 121.3(4) 108.1(4) 130.6(4) 121.1(4) 107.5(4) 131.3(4) 118.6(4) 121.7(4) 119.7(4) 119.4(4) 121.4(4) 119.2(4) 120.4(5) 119.9(5) 121(3) 119(3) 120.1(5) 119(3) 121(3) 119.9(5) 120.5(5) 120(3) 120(3) 121.2(5) 123(4)

C(14B)-C(13B)-H(13B) C(13A>C(14A>C(15A) C(13A>C(14A)-H(14A) C(15A)-C(14A)-H(14A) C(15B)-C(14B>C(13B) C(15B>C(14B>H(14B) C(13B>C(14B)-H(14B) C(14A)-C(15A)-C(10A) C(14A)-C(15A)-H(15A) C(1OA)-C(15A)-H(15A) C(14B>C(15B)-C(10B) C(14B)-C(15B>H(15B) C(10B)-C(15B>H(15B)

116(4) 119.7(5) 120(3) 120(3) 119.0(5) 121(3) 120(3) 120.7(5) 120(3) 120(3) 120.5(5) 122(3) 118(3)

Table 3 . Structure of the molecule III. Atomic coordinates (* 104) and equivalent temperature factors Ueq (A2*103) defined as one third of the trace of the orthogonahzed Uy tensor.
Atom N(l ) C(2) O(2) C(3) C(4) C(5) C(6) C(7) C(8) O(81) O(82) C(9) C(10) C(ll ) C(12) C(13) C(14) C(15) C(16) H(3) H(4) H(5) H(6) H(71) H(72) H(10) H(ll ) H(12) H(13) H(14) H(151) H(152) H(153) H(161) H(162) H(163) X 5965(2) 6664(2) 7745(2) 6038(3) 4925(3) 4336(3) 4868(3) 6468(2) 5405(2) 6129(2) 5268(2) 3795(2) 3531(3) 2097(3) 913(3) 1162(3) 2596(2) 5369(4) 6618(3) 6497(29) 4526(31) 3526(30) 4518(26) 6536(20) 7494(23) 4379(27) 1914(26) -96(30) 363(28) 2804(23) 4460(34) 6062(36) 5254(40) 6296(27) 6962(31) 7420(32)
Y Z

3203(2) 2304(2) 1612(2) 2286(3) 3124(3) 4066(3) 4082(3) 3268(2) 2521(2) 2745(2) 1159(1) 3085(2) 4343(2) 4910(3) 4229(3) 2988(3) 2410(2) 2165(3) 372(3) 1644(25) .. 3091(28) 4708(28) 4717(24) 4211(22) 2873(20) 4805(24) 5761(27) 4638(26) 2510(26) 1567(22) 2564(31) 2283(32) 1193(39) -513(30) 301(29) 693(30)

7188(1) 6649(2) 6960(1) 5742(2) 5427(2) 5989(2) 6847(2) 8139(1) 8721(1) 9585(1) 8521(1) 8616(1) 8948(2) 8834(2) 8377(2) 8044(2) 8164(2) 10286(2) 8674(2) 5373(17) 4793(20) 5809(17) 7270(16) 8314(12) 8219(13) 9269(16) 9063(16) 8302(17) 7700(17) 7915(13) 10326(20) 10847(23) 10228(23) 8477(16) 9315(21) 8342(19)

38(1) 44(1) 59(1) 56(1) 65(1) 61(1) 48(1) 37(1) 34(1) 42(1) 41(1) 33(1) 43(1) 52(1) 56(1) 53(1) 42(1) 56(1) 54(1) 66(8) 85(9) 75(8) 57(7) 34(5) 36(5) 60(7) 61(7) 73(8) 69(8) 40(6) 85(10) 102(11) 121(13) 68(8) 88(10) 84(9)

Table 4. Structure of the molecule III. Bond lengths [A] and angles [cleg].

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N(1>C(6) O(82)-C(16) N(l)-C(2) C(9>C(14) N(l)-C(7) C(9)-C(10) C(2)-O(2) C(1O>C(11) C(2>C(3) C(10)-H(10) C(3>C(4) C(ll)-C(12) C(3)-H(3) C(ll)-H(ll ) C(4)-C(5) C(12>C(13) C(4>H(4) C(12)-H(12) C(5>C(6) C(13>C(14) C(5>H(5) C(13)-H(13) C(6>H(6) C(14)-H(14) C(7)-C(8) C(15>H(151) C(7)-H(71) C(15)-H(152) C(7)-H(72) C(15)-H(153) C(8)-O(82) C(16)-H(161) C(8)-O(81) C(16>H(162) C(8)-C(9) C(16)-H(163) O(81)-C(15) C(6)-N(l)-C(2) C(8)-O(82)-C(16) C(6>N(1)-C(7) C(14)-C(9)-C(10) C(2)-N(l)-C(7) C(14)-C(9)-C(8) O(2)-C(2)-N(l) C(10>C(9)-C(8) O(2)-C(2>C(3) C(ll)-C(10)-C(9) N(1>C(2>C(3) C(11)-C(1O>H(1O) C(4)-C(3>C(2) C(9)-C(10>H(10) C(4)-C(3)-H(3) C(12>C(ll)-C(10) C(2)-C(3)-H(3) C(12)-C(11>H(11) C(3>C(4)-C(5) C(10)-C(ll)-H(ll ) C(3)-C(4)-H(4) C(13)-C(12)-C(ll) C(5)-C(4>H(4) C(13)-C(12>H(12) C(6)-C(5>C(4) C(11)-C(12>H(12) C(6)-C(5)-H(5) C(12>C(13>C(14) C(4>C(5)-H(5) C(12VC(13)-H(13)

1.373(3) 1.428(3) 1.398(3) 1.382(3) 1.469(3) »1.387(3) 1.236(3) 1.382(3) 1.433(3) 0.97(2) 1.345(4) 1.379(3) 0.97(3) 0.94(3) 1.403(4) 1.370(4) 0.99(3) 0.98(3) 1.342(3) 1.387(3) 0.98(3) 0.96(3) 0.97(2) 0,95(2) 1.539(3) 0.90(3) 0.98(2) 1.01(3) 0.98(2) 0.98(4) 1.403(2) 0.97(3) 1.420(2) 0.99(3) 1.522(3) 0.96(3) 1.431(3) 121.8(2) 116.7(2) 118.6(2) 118.7(2) 119.5(2) 122.1(2) 120.3(2) 119.2(2) 125.0(2) 120.8(2) 114.7(2) 121.2(14) 122.3(3) 118.0(14) 123(2) 119.9(2) 115(2) 119(2) 120.4(3) 121(2) 120(2) 119.7(2) 120(2) 121(2) 118.7(3) 119(2) 116(2) 120.5(2) 125(2) 121(2)

C(5)-C(6)-N(l) C(14)-C(13>H(13) C(5>C(6>H(6) C(9>C(14>C(13) N(l)-C(6)-H(6) C(9>C(14>H(14) N(1)-C(7>C(8) C(13)-C(14>H(14) N(1)-C(7>H(71) O(81>C(15>H(151) C(8>C(7)-H(71) O(81)-C(15)-H(152) N(1)-C(7>H(72) H(151)-C(15>H(152) C(8)-C(7)-H(72) O(81>C(15>H(153) H(71)-C(7>H(72) H(151)-C(15)-H(153) O(82>C(8>O(81) H(152>C(15>H(153) O(82>C(8>C(9) O(82>C(16>H(161) O(81>C(8>C(9) O(82)-C(16>H(162) O(82)-C(8>C(7) H(161)-C(16)-H(162) O(81)-C(8)-C(7) O(82)-C(16)-H(163) C(9)-C(8)-C(7) H(161)-C(16)-H(163) C(8)-O(81>C(15) H(162)-C(16)-H(163)

121.8(3) 118(2) 122.8(14) 120.3(2) 115.3(14) 117.8(12) 113.3(2) 121.8(12) 108.2(11) 110(2) 109.9(11) 107(2) 107.1(11) 111(3) 109.5(12) 113(2) 109(2) 111(3) 112.1(2) 104(3) 106.2(2) 104(2) 111.8(2) 112(2) 113.3(2) 107(2) 101.8(2) 112(2) 111.7(2) 111(2) 114.8(2) 111(2)

EXPERIMENTA L 2-Phenvloxazolo[3.2-alpyridinium perchlorate (II) [1,2] was prepaired according t o the modified method described early [9]. 1 -[ 1.1 -dimethoxy-1 -phenvlethvl-21pyridone-2 (III). 0.3 g (1 mmol) of the perchlorate II was dissolved in 15 ml of the solution of MeON a in MeO H (prepared from 0.03 g (1.3 mmol) of N a and 15 ml o f MeOH) . The mixture was stirred a t 20°C for 2 hours and kept overnight. After evaporation of the solvent the residue was purified by column chromatography (SiO2, CH2C12) giving 0.25 g (95%) of ketal III, M.p . 142144°C. Calculated (%): C 69.58 , H 6.61 , N 5.40. C15H17NO3. Found (%): C 70.15 , H 6.63 , N 5.43. NM R ' H (400 MHz, CDC13, 8, ppm): 7.35-7.25 (5H, m, Ph), 7.11 (1H, dd, H-4 , J34 9.2 Hz , J4S 6.7 Hz) , 6.72 (1H, d, H-6 , J56 6.9 Hz) , 6.33 (1H, d, H-3 , J34 9.2 Hz) , 5.82 (1H, dd, H-5 , J45 6.7 Hz , J45 6.7 Hz , J56 6.9 Hz) , 4.37 (2H, s, CH2), 3.33 (6H, c, CH3O). NM R 13C (400 Mhz, CDC13, 8, ppm): 162.53 (C2=O); 139.14, 138.28 (C4, C6); 137.93 (C , Ph) ; 128.60, 128.30, 127.48 (CH, Ph) ; 120.74 (C3); 104.96 (C5), 102.60 (C , (0Me) 2 ) ; 51.34 (OMe), 49.64 (CH2).

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In the analogous conditions 1phenacylpyridone-2 (IV) does not form the ketal III even after a week (TLC control). Only after a month of keeping some traces of III have been registered in the reaction mixture. Crystal structure of II. Ci3H10ClNO5, Mr =295.67, triclinic, P-l , a=5.762(l), b=14.469(3), c=16.598(4)A, a= l 12.53(2), P=83.35(2), y=90.29(2)°, V=1268.5(5)A3, Z=4, Dx=1.548 g/cm"3. Prismatic crystal with dimention 0.45x0.25x0.25 mm. Lattice parameters refined using 25 reflections in the range 12°<9<16°. CAD-4 four circle diffractometer, graphite monochromatized MoK« radiation. 4443 measured reflections, with 9max=25°; -62a(I) and R=0.1215, wR2=0.1501 for all data. Final maximum shift to error = 0.01. Maximum and minimum height in final difference fourier synthesis 0.405 and -0.303 e.A3. Atomic coordinates are in Table 1, bond lengths and angles are in Table 2. Crystal structure of III. C15H17NO3, Mr = 259.29, monoclinic, P2,/c, a=8.812(2), b=10.036(l), c=15.152(2)A, p=95.32(2)°, V=1334.2(4)A3, Z=8, Dx=1.291 g/cm"3. Prismatic crystal with dimention 0.35x0.30x0.25 mm. Lattice parameters refined using 25 reflections in the range 12°2a(I) and R=0.0813, wR2=0.1164 for all data. Final

maximum shift to error = 0.01. Maximum and minimum height in final difference fourier synthesis 0.187 and -0.164 e.A3. Atomic coordinates are in Table 3, bond lengths and angles are in Table 4. ACKNOWLEDGEMENTS This work was funded by the Russian Foundation of Basic Research (Grants 96-03-32953 and 96-07-89187) and by the Grant Center for Natural Sciences (GRACENAS, St.Petersburg, Grant 95-0-9.4-222). REFERENCES 1. C. K. Bradsher, M. Zinn, J. Heterocycl. Chem. 1967, 4, 66 - 70. 2. H.Pauls, F.Krohnke, Chem. Ber. 1976,109, 3646 - 3652. 3. A. R. Katritzky, A. Zia, J. Chem. Soc. Perkin Trans. 71982, 1 , 131 -136 . 4. G. Markl, S. Pflaum, Tetrahedron Lett. 1988, 28, 1511-1514 . 5. E. V. Babaev, K. Yu. Pasichnichenko, D. A. Maiboroda, Khim. Geterotsikl. Soedin. (in Russian) 1997, 3, 397 - 402. 6. E. V. Babaev, S. V. Bozhenko, D. A. Maiboroda, Russ. Chem. Bull. (Engl. Ed.) 1995, 44, 2203. 7. E. V. Babaev, S. V. Bozhenko, Khim. Geterotsikl. Soedin. (in Russian) 1997, 1 , 141 - 142. 8. E. V. Babaev, A. V. Efimov, D. A. Maiboroda, K. Jug, Liebigs Ann.Chem., 1997, 1 , (inpress). 9. E. V. Babaev, A. V. Efimov, D. A. Maiboroda, Chem. Heterocycl. Compounds (Engl. Transl), 1995, 8, 962 ~ 968. (Original: Khim. Geterotsikl. Soedin. pp. 1104-- 1111.) 10. W.D.S. Motherwell, W. Clegg, PLUTO Program for Plotting Molecular and Crystal Structures. 1978, Univ. of Cambrige, England. 11. G. M. Sheldrick, SHELXS86 Program for the Solution of Crystal Structures, 1985, Univ. of Gottingen, Germany. 12. G. M. Sheldrick, SHELXL93 Program for the Crystal Structures Refinenent, 1993, Univ. of Gottingen, Germany.

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