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Abstract:
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Carbon-carbon and carbon-heteroatom bond formations constitute the
central events in organic synthesis. In view of this, much of the research in
organic synthesis has been focused on devising novel and efficient methods for
such bond constructions. In general, polar, pericyclic and radical methodologies
are employed for this purpose. The polar and radical reactions proceed via
reactive intermediates such as carbanions, enols/enolates, enamines, carbocations,
radical cations, radical anions, carbenes, zwitterions etc. In recent years, there has
been enormous interest in the chemistry of zwitterionic species largely from the
standpoint of their applications in multicomponent reactions (MCRs) and
organocatalytic reactions. Zwitterions formed by the addition of nucleophiles to
electrophilic π-systems such as acetylenic esters and azoesters have been the
subject of extensive investigations; their synthetic utility, however, remained
largely unexplored. Investigations in a number of laboratories, including our own,
have shown that zwitterions of the type mentioned above on reaction with
electrophiles give rise to carbo- and heterocyclic products by 1,3- or 1,4-dipolar
cycloadditions. Recently, allenoates, another class of active π-systems were
introduced to this field. Against this background, a systematic investigation of the
reactions of various zwitterions derived from allenoates with different
electrophiles especially 1,2-diones, were carried out. The results of these studies
are embodied in the thesis entitled “Novel Synthesis of Carbocycles and
Heterocycles Employing Zwitterions Derived from Allenic Esters”. |