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6-tetrahydropyridinium quaternary salts which have a benzoylmethyl or ethoxycarbonylmethyl group on atom N-1 generate N-ylides when heated in the presence of NaH and they can rearrange in situ with contraction or expansion of the six-membered heterocycle to give substituted pyrrolidines (as a result of a [2,3]-sigmatropic rearrangement) or 1H-tetrahydroazepine derivatives (via Stevens rearrangement). The presence of an aryl substituent at position C-4 in the tetrahydropyridine ring allows to avoid the formation of elimination products and changes the direction of the reaction towards the preparation of the tetrahydroazepines.In the presence of base, N-methyl-N-phenacyl-1,2,3,6-tetrahydropyridinium halides are converted to N-ylide systems which can rearrange with contraction of the six-membered heterocycle to five-membered forming N-alkyl-2-benzoyl-3-vinylpyrrolidines [1, 2]. Exchange of the N-phenacyl fragment in the starting quaternary tetrahydropyridinium salts for N-(alkoxycarbonyl)methyl also stabilizes the intermediate ylides and leads to derivatives of the natural α-amino acid proline [3][4][5][6][7] which may be important from the viewpoint of biological activity. Key features in the studies [1-7] are as follows: firstly only C-unsubstituted tetrahydropyridines were used as the basic starting materials; secondly a high diastereoselectivity (95%) was found in the substituted pyrrolidines formed; and finally the basic electrophilic [2,3]-sigmatropic rearrangement was accompanied by up to 45% β-elimination with opening of the heterocycle and the formation of dialkylaminopenta-2,4-dienes.In connection with our systematic investigation of the chemistry of 4-aryl-substituted tetrahydropyridines and related compounds [8,9] we decided to study the effect of an aryl substituent in the quaternary tetrahydropyridinium salts on the route of their reaction in the presence of base.

Organo-boron compounds S 0040Synthesis and Molecular Structure of 2,4,8a-Triaryl-6-methylperhydro[1,3,2]dioxaborinino[5,4-c]pyridines. -Condensation of 1,3-diol (I) with arylboronic acids affords the title compounds (III), which are representatives of a new heterocyclic system. Their stereochemistry and molecular structures are established by single crystal X-ray diffraction analysis. -(LE TUAN ANH; POLYANSKII, K. B.; ANDRESYUK, A. N.; SOLDATENKOV*, A. T.; MAMYRBEKOVA, Z. A.; KULESHOVA, L. N.; KHRUSTALEV, V. N.; Russ. Chem. Bull. 53 (2004) 4, 842-845; Russ. Peoples' Friendship Univ., Moscow 117198, Russia; Eng.) -D. Singer 03-165