Dehydrobenzooxepanes by Tandem Nicholas Reactions
Benzo- fused seven membered ring ethers, or benzooxepanes, are widely encountered structures within natural products such as the heliannuols. We intend to target the synthesis of this ring system by of employing derivatives of butyne-1,4-diol-Co2(CO)6 complexes, by way of tandem Nicholas reactions with para- substituted phenols, thereby constructing the seven- membered ring system. Variation between the possibilities of forming the arene ortho- carbon - propargyl carbon bond initially and the phenolic oxygen - propargyl carbon bond subsequently, and the reverse arrangement of order, will be investigated. In addition the possibility of one-pot 4+3 cycloaddition protocol will be addressed. The suitability of various substituents in the benzene and the seven membered ring will be studied, with particular attention to incorporation the benzylic methyl group common to the heliannuols in enantiomerically enriched form. Methods of reductive removal of the Co2(CO)6 unit will be investigated, to give the more stable oxacycloalkenes or oxepanes.