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

摘要

Methods are described for conversion of a series of (E)-alka-(omega-3),(omega-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,(omega-3),(omega-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. [References: 32]