Synthesis and some chemical properties of 4-acyl-2,6-disilapiperazines. Molecular and crystal structure of 4-formyl-2,2,6,6-tetramethyl-2,6-disilapiperazine

Abstract

The increased activity of pentacoordinated silicon compounds relative to the corresponding tetrahedral analogs in nucleophilic substitution reactions is reflected in a review of the possibility of their wide use for synthetic purposes [1]. In particular we have previously synthesized the almost unstudied earlier heterocyclic systems -the l-oxa-4-aza-2-silacyclanes from N-monodimethylchlorosilylmethyl derivatives of amides [2-4], and we have obtained 4-acyl-2,6-disilamorpholines for the first time from N,N-bis(dimethylchlorosilylmethyl)amides [2, 5].In development of these investigations in the present work we have synthesized 4-acyl-2,6disilapiperazines, studied some of their chemical reactions, and studied one of them by X-ray diffraction analysis method. It should be noted that silicon-containing derivatives of piperazine are of interest with respect to their specific reactivity, their biological activity, and the possibility of using them in practice (see, for example, the review [6] and references cited in it).The proposed route for the synthesis of 4-acyl-2,6-disilapiperazines is based on the high disposition to cyclocondensation ofpentacoordinated dimethyl(amidomethyl)chlorosilanes with an additional functional group at the amide nitrogen atom. We previously used this approach to obtain 4-acyl-2,6-disilamorpholines [2, 5]. Carboxamides, which were converted into the corresponding N,N-bisdimethylchlorosilylmethyl derivatives by reaction with dimethylchloromethylchlorosilane/hexamethyldisilazane, served as the starting materials. These intermediate derivatives were hydrolyzed to the required disilamorpholines without isolation from the reaction mixture.Following the above strategy and one-pot technique but using ammonolysis reaction (with ammonia or primary amines) in place of hydrolysis, we have synthesized 4-acyl-2,2,6,6-tetramethyl-2,6-disilapiperazines Ia,b and Ha, b, which differ from those described in [6] by the presence ofacyl group in position 4 of the piperazine ring.