Synthetic studies towards virantmycin.

The use of vinylphosphonium salts in the construction of acyclic and cyclic systems by both ourselves and others is reviewed.The alkylthio and arylthio vinylphosphonium salts are used in an unsuccessful approach to the synthesis of the tetrahydroquinoline natural product virantmycin.The use of this approach in the early stages of a synthesis of carbaprostacyclin and analogues is also examined.The synthesis of virantmycin was also investigated using a regioselective Dieckmann reaction. Two procedures have been developed for the synthesis of the mixed 0,S-diester required to study the cyclisation. The first of these has as the key step a one carbon homologation reaction of a benzaldehyde to a phenylacetic acid derivative. The second relies on a pericyclic rearrangement reaction. The latter route has proved more successful and the Dieckmann product has been made using this procedure. Applications of this to the synthesis of virantmycin are discussed.The use of methyl methylsulphinylmethyl sulphide in the one carbon homologation for the synthesis of the Dieckmann precursor has been extended. Thus a set of conditions has been developed for the synthesis of chloroketenedithioacetals from ketenedithioacetal S-oxides which complements the only other known set of conditions for this transformation. Under our conditions the ketene dithioacetal S-oxide derived from 2-aminobenzaldehyde cyclises to give two indoles. A modified set of conditions are presented which give rise to anomalous products. In the light of this a mechanism is proposed.Finally the use of this strategy is extended to a synthesis of benzofurans and further discussion shows how this might be used in a general preparation of thiol esters and in the synthesis of other heterocyclic systems or natural products.