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Chemistr)' of Hetetwr

Compounds. ~'ol. 36, No. 3. 2000

HETEROCYCLES

WITH A BRIDGED

NITROGEN ATOM. 12". RECYCLIZATION OF 5-METHYLOXAZOLO[3,2-a]PYRIDINIUM CATION IN THE PRESENCE OF ACETYLACETONE. CRYSTAL STRUCTURE OF I-ACETYL-

2,5-DIMETHYLINDOLIZINE*-'

E. V. Babaev, A. V. Efimov, B. V. Rybakov, and S. G. Zhukov

Reaction oJ" 5-met/tyl-2-(p-nitrophenyl)o.tazolo[3.2-a]pyridinittm perch~or.ate with acetvlacetone gives I-acetvl-2,5-dimethylindolizine, the strltctttre of" which was proved by X-ray attalvsis.
Keywords: indolizine, pyridine, pyrrole, X-ray diffraction analysis. We have previously reported two novel strategies for building up the indolizine skeleton by the recyclization of oxazolol3,2-alpyridinium salts. In the first case (strategy A) the pyrrole ring is formed by two carbon atoms of acetylacetone and the C,,,NC,,,, sequence in the starting cation [2]. In the second case (strategy B) the pyrrole ring is present in a hidden form in the skeleton of the starting bicycle as the C,,,C,,,NC,,, sequence and the methyl group at position 5 I3]. It was of interest to study such a combination of reagents in which these two strategies can occur together. If oxazolopyridinium cation containing 5-CH, group is introduced into the reaction with acetylacetone then both strategies A and B become equally likely.

(Ac),CHNa

~

~()
]

+
HNR 2

NR2

I

/~'-'-A r

o

,,r

,

O

O

N

0

Ar

* For communication I I see [ 1]. ,2 Dedicated to the anniversary of Professor M. A. Yurovskaya. M. V. Lomonosov State University, Moscow 119899, Russia; e-mail: babaev@org.chem.msu.su. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 401-405, March, 2000. Original article submitted March 15, 1999. 0009-3122/00/3603-0339525.009 KluwerAcademic/Plenum Publishers 339


We have found that the reaction of 5-methyl-2-(p-nitrophenyl)oxazolo[3,2-alpyridinium perchlorate (1) with acetylacetone in methanol solution of sodium methylate gives l-acetyl-2,5-dimethylindolizine (2). The structure of the compound obtained was proved by X-ray analysis (see Fig. 1).

(-)~Mc
+

I.
Me

/2---S
CIOI I

Mc ~ ()~ ~'~NO, O

( Ac)_,CII: MeONa/MeOIt
0

~
Me

1

3.
Mc

Me

3b

This reaction is accompanied, not altogether obviously, by the elimination of an aryl residue from the starting structure. The probable mechanism of this process includes formation of the open form 3a, in which closing of the pyrrole ring to indolizine 31+ occurs with elimination of the p-nitrobenzoyl group to form indolizine 2. The driving force for the elimination is apparently the steric interaction between the p-nitrobenzoyl group at position 3 and the 5-CH, group of intennediate 3b. We note that deacylation of 3-acylindolizines [4] (in particular 3-acyl-5-methyl derivatives [5]) under the action of base is well known. Hence, in the example studied, the scheme A is realized and the pyrrole ring is built up from oxazole with one basic difference, i. e., elimination of acyl fragment and this is, in fact, due to the presence of the methyl group in the starting substrate.

r

/

9d

,H

|

H!C? -i

/.'

"@~

Fig. 1. Numbering of the atoms and the structure of compound 2.

340


TABLE 1. Atomic Coordinates (x l0 ~) and Equivalent Isotropic Parameters (U~q · l0 s) in the Investigated Structure
Atom
Ctl~ C,2: Ct~) CI5~ (-'r 7~ Cts~
Nful

v 311214) 2336(4) 51(1(3/ 266(31 -1156(41 -94514) 70214) 2108(4) ~886(3) 3880(5) 3329(5) -907(4) -564(7) -2433(3) 4252(44) -2203(421 -1946(42) 817(39) 4219(45) 4790151) 3848(501 3270(39) 2799(46) 4638(59) 302(59) -10(701 -1652(62) 5729(2) 5145(2) 5512(21 6329(2) 7016(3) 7760(3) 7839(3) 7185(21 6456(2) 7186(41 4278(4) 5149(31 4302(5) 5529(2) 5706(25) 6944(24) 8200(25) 8368(26) 6348(33) 7474(32) 7712(351 4477(25) 3489(31) 4237(33) 4644(34) 3532(45) 4228(36)
6215(21 6082(2) 6770(21 5854(2) 5261(31 4400( 3 ) 4066(3) 4616(21 551 l(2) 4295(4) 7830(3) 7331(21 8329(4) 6993(2) 6096(231 5535(24) 3962(241 3425(251 4144(26) 4975(30) 3622(35) 8636(27) 7716(271 7834(30) 8929(36) 8177(39) 8570(34) 53( I ) 53( l ) 50( l ) 47( I ) 57(I) 64( I ) 60( I ) 52(I) 47( I) 69( I ) 72(I) 60( I ) 86( I ) 79( I ) 69(9) 69(9) 68(8) 75(9) 95111) I01(12) 111(13) 69(9) 83(I l) 113(131 113([5) 156(201 116(14)

Cr
(~'1 [ j i

~.'1121 CII31 O~1~

H,I, H,., 11,,.
Hi71

H, Io2 ) H~,o~, I-I,j,,,
Hill21

H. t31

H,,m

H,,3.,,

TABLE 2. Bond Lengths (d) in the Molecule of the Investigated Compound
Bond
Ct E~-Ci2

d, A
1.353(41 1.386(31 1.439(4) 1.487(41 1.398(41 1.45(1(4) 1.399(31 1.403(41
Cc,)-Ctf, i

Bond

d, A
1.349(4) 1.410(4) 1.357(41 1.373(31 1.493(41 1.238(41 1.493(5)

C(6~-Cc7~ Cc8)-NIm C, j2wOm C._.r-C.~

C,:, C~, C~ C,~, C,.,

C.u C,~ C, J2~ N,,,, C,,,

EXPERIMENTAL Reaction of 5-Methyl-2-(p-nitrophenyl)oxazolo[3,2-a]pyridinium Perchlorate 1 with Acetylacetone. Acetylacetone (6 ml, 60 mmol) was added to solution of perchlorate 1 (0.1 g, 0.3 retool) in methanol (20 ml) containing sodium methylate (4 mmol) and the product was held at room temperature. The conversion degree was monitored by TLC from the growth in intensity of the indolizine spot (developed using the Ehrlich reagent). The best yield was achieved with an extremely prolonged (100 days) holding off the reaction mixture at 20~ (brief heating leads to significant tarring and formation of a mixture of reaction products). The reaction mixture was filtered and the filtrate was evaporated and chromatographed on SiO, column with chloroform as the eluent to givel-acetyl-2,5-dimethylindotizine 2; mp t27~ Monocrystals for X-ray analysis were prepared by slow 341


TABLE 3. Bond Angles (co) in the Molecule of the Investigated Compound
Angle
(,), deg.

Angle

t,), deg.
12(I.4( 3 ) 120.713 } 118.2(3) 124.2(31 117.6(3) 129.1(21 123.0(2 ) I(17.9121 120.9(31 11K4t3)

C<..~ Cm N++~ Cu, C,:, Cn, Cm C+2~C'.t~

I I(}.()12} I(17.4121

121.9131
130.Xl 3 ) I(17 All 2 )

C,~, C,3,~,t.., C,:rCnFC, t:b Cc~+ C~4+Cf+~ C+, C,s,~r Co~ C,~.+ C,~a~

122.9(2 )
13(I.213 )

C,~ Cqs, s ('nr N,~,; C,.~

C.,, ('r.J C,s, C,s, C',~ N~,~

C,~ C,., N,,.. C,.. C,.,, Cm

1(17.712) 135.3(31 I 17.0(21 1 20J~( 3 ) 12(I.713)

C,,, N,.~, C,,, Oftl ('clZ~ Cf~l 0,~, Cnz~ (',~,

evaporation of chlorofoml solution at 4~ 'H NMR spectrum (400 MHz, DMSO-d,,): 8.14 (IH, d, ,17, = 10 Hz, ` 8-H): 7.28 (IH, s, 3-H): 7.13 (IH, dd, ,I,.7 =9 Hz, .1:., = I0 Hz, 7-H): 6.49 (IH, d, J,,: = 9 Hz, 6-H): 2.56 (3H, s, I-COCHy; 2.50 (3H, s, 5-CH,); 2.48 ppm (3H, s. 2-CH,). For protons of the 2- and 5-CH, groups the signal assignment may be reversed. X-Ray Structural Investigation of Compound 2 was carried out on a CAD-4 automatic monocrystal diffractometer using ~.MoK, irradiation. Unit cell parameters were determined in the range of 15-16 0 angles for 25 reflections. Crystals of the studied compound were assigned to the monoclinic syngony (space group P2,/n) with unit cell parameters a = 7.721(6L b = 11.096(2). c = I 1.869(5) ,~; ~3 = 101.76(5)~ Z = 4. The structure was solved by direct methods using the SHELXS-97 complex program [6] and refined by a full-matrix, least-squares analysis via the SHELXL-97 program [7] in the anisotropic approximation for non-hydrogen atoms. All of the hydrogen atoms were localized from differential Fourier synthesis of the electron density and refined isotropically. The final R- factor was 0.0600 for 1956 independent reflections with 1 > 2a (/). Positional parameters for the atoms in the investigated compound and isotropic thermal parameters equivalent to the corresponding anisotropic ones are given in Table I and interatomic distances and bond angles reported in Tables 2 and 3. The spatial disposition of the atoms in the molecule and their numbering are given in Fig. 1181. This work was carried out with the support of the RFFR (grant 99-03-33076a). The authors also express their thanks to the RFFR for financial support in paying for the license to use the Cambridge structural data bank (project No. 96-07-89187).

REFERENCES
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2. 3. 4. 5. 6. 7.

8.
342

E. V. Babaev, A. V. Efimov, V. B. Rybakov. and S. G. Zhukov, Khim. Geterotsikl. Soedin, No. 4, 550 (1999). E. V. Babaev and S. V. Bozhenko, Khim. Geterotsikl. Soedin., No. 1, 141 (1997). E. V. Babaev, A. V. Efimov, S. G. Zhukov, and V. B. Rybakov, Khim. Geterotsikl. Soedin., No 7, 983 (1998). E. T. Borrows, D. O. Holland, and J. Kenyon, J. Chem. Soc., No 11, 1083 (t946). J. W. Dick, W. K. Gibson, D. Leaver. and J. E. Rolf, J. Chem. Soc., Perkin. Trans. 1, No. 12, 3150 ( 1981 ). G. M. Sheldrick, SHELXS-97, Program for the Solution of Crystal Structures, University of GOttingen, Germany, 1997. G. M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures, University of GOttingen, Germany, 1997. A. L. Spek, PLUTON-92, Molecular Graphics Program, University of Utrecht, The Netherlands, 1992.