Studies of Some Strained Organic Molecules

Abstract

The studies described in this thesis comprise three distinct aspects of cycloproparene chemistry. The first part of the work addresses the preparation of alkylidene-1H-cyclopropa[b]naphthalene-3,6-diones (132) from the corresponding 3,6-dimethoxy homologues in order to form "push-pull" electronic systems. This study required the synthesis of 1H-cyclopropa[b]naphthalene-3,6-dione (144). This cyclopropaquinone is stable and is the first to be characterised; its reactions are discussed. The compound exhibits typical quinine-like properties and under mild conditions reacts at the quinone C4-C5 double bond rather than the strained "cyclopropene” ring. Efforts to prepare the oxygen containing 3,6-dimethoxy-1 H-cyclopropa[b]anthracene (134), and its dicyclopropa-homologue (135) have also been examined in order to test the suitability of gem-dihalobicyclo[4. 1.0]heptenes as precursors to such molecules. The second component of the work addresses Diels-Alder cycloaddition reactions of diarylmethylidenecyclopropabenzenes (92a,b) and compares the results with those obtained using the naphthalene analogues. The regioselectivity found for the benzene derivatives is addition to the endocyclic bond to give stereoisomer (189) only. In contrast, the naphthalene homologues react at the exocyclic bond; the results are in accord with a theoretical analysis. The use of a hydrophilic solvent (ethylene glycol) leads to a two to three fold increase in reaction rate over reactions in toluene. The third section describes attempts to prepare C2-substituted alkylidenecyclopropa[b]naphthalenes (138) with the ultimate aim of introducing polar or conjugating substituents at this position. Three possible routes have been explored using disilyl (108), the methylidene derivatives (93a,b) and the 1H-cyclopropa[b]naphthalene precursor (214), but none was successful.