Aspects of free radical cyclisation

Caddick, Stephen (1989) Aspects of free radical cyclisation. University of Southampton, Doctoral Thesis.

Abstract

A model study was carried out to investigate the use of a novel 1,5 allylic abstraction-cyclisation reaction, in a proposed synthesis of the ring skeleton of the Pentalenolactone group of structures. The model study led to isolation of a product resulting from a stereospecific 6-exo-trig radical cyclisation. A new 1,5 allylic abstraction-cyclisation reaction has been developed, which has been used for the synthesis of 6,5 bicyclic ring systems, a spirocyclic ring system and cyclic ring systems. The analysis of results and possible implications are discussed. The development of a new synthetic method for the construction of both carbocyclic ring systems and oxygen containing heterocyclic ring systems was investigated. This method was based upon a 1,6 allylic abstraction-cyclisation reaction. The syntheses of the required precursors proved problematic but were eventually prepared in poor yield. Treatment of the various precursors under a variety of radical conditions did not lead to the any of the desired cyclisations. Some 1,6 and 1,7 diene systems were prepared and were found to undergo radical stannylation-cyclisation reactions, on treatment with tri-n-butyl and triphenyltin hydride. An interesting regiospecific cyclisation resulted from one of these investigations. Removal of the tin group from the cyclised products could not be effected.(DX889571)

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