Intramolecular Diels-Alder reactions of 1-phenylsulfonylalka-1,2,(omega-3),(omega-1)-tetraenes

Methods are described for conversion of a series of (E)-alka-(omega-3),(ome ga-1)-dienals 2, via ethynylation to the corresponding alkadienynols 3, fol lowed by sequential [2,3] sigmatropic rearrangement of their derived phenyl sulfenate esters and chemoselective oxidation, into 1-phenylsulfonylalka-1, 2,(omega-3),(omega-1)-tetraenes 5, which are used to study the influence of tether length and peripheral substitution upon intramolecular cycloadditio n reactivity and selectivity. It is demonstrated that (6E)-1-phenylsulfonyl nona-1,2,6,8-tetraene 5c and substrates featuring an analogous ethylene lin kage between the functional termini, display exceptionally high intramolecu lar Diels-Alder (IMDA) reactivity, accompanied by exo-diastereoselectivity. Comparative studies are described, which delineate structure-reactivity tr ends and demonstrate the unique capacity of the dienophilic allenyl terminu s to impose reactivity-enhancing conformational constraints upon IMDA proce sses in favourable cases. Preliminary investigations into substrates incorp orating cyclic dienyl substructures are reported, and a novel approach to s piro[4.5]decanoid ring systems is described.