Intramolecular Diels–Alder reactions of 1-phenylsulfonylalka-1,2,(ω − 3),(ω − 1)-tetraenes

Abstract

Methods are described for conversion of a series of (E)-alka-(ω − 3),(ω − 1)-dienals 2, via ethynylation to the corresponding alkadienynols 3, followed by sequential [2,3] sigmatropic rearrangement of their derived phenylsulfenate esters and chemoselective oxidation, into 1-phenylsulfonylalka-1,2,(ω − 3),(ω − 1)-tetraenes 5, which are used to study the influence of tether length and peripheral substitution upon intramolecular cycloaddition reactivity and selectivity. It is demonstrated that (6E)-1-phenylsulfonylnona-1,2,6,8-tetraene 5c and substrates featuring an analogous ethylene linkage between the functional termini, display exceptionally high intramolecular Diels–Alder (IMDA) reactivity, accompanied by exo-diastereoselectivity. Comparative studies are described, which delineate structure–reactivity trends and demonstrate the unique capacity of the dienophilic allenyl terminus to impose reactivity-enhancing conformational constraints upon IMDA processes in favourable cases. Preliminary investigations into substrates incorporating cyclic dienyl substructures are reported, and a novel approach to spiro[4.5]decanoid ring systems is described.