Diels-Alder Reactions of S-Vinyl-S-Arylsulfoximines

Cyclopentadiene and the known S-p-tolyl-S-vinyl-A-phthalimidosulfoximine (1a) undergo Diels-Alder reaction to give a mixture of cycloadducts in excellent yield. The structures of the cycloadducts including stereochemistry are assigned by ¹ H NMR spectroscopy. The crystal and molecular structure of the major cycloadduct 5d, n = 1, G = 1,2-C₆ H₄(CO)₂ N was determined unequivocally by X-ray crystallographic techniques. Treatment of this major cycloadduct with hydrazine in ethanol resulted in conversion of the sulfoximine to sulfoxide group concomitant with reduction of the carbon-carbon double bond. Use of allyl alcohol as solvent in this reaction allowed conversion to the corresponding unsaturated sulfoxide 8. The previously unknown S-p-tolyl-S-vinyl-N-(p-tolylsulfonyl)-sulfoximine (1b) is somewhat more reactive than phenyl vinyl sulfone and undergoes Diels-Alder reactions with cyclic and acyclic 1,3-dienes in 81-95% yield. The endo selectivity of vinylsulfoximine 1b is 9:2 with cyclopentadiene and 93:7 with 1,3-cyclohexadiene. With 2-methyl-1,3-butadiene the para adduct is produced regioselectively in a ratio of 4:1. Although formation of the endo adducts from vinylsulfoximine 1b and “cyclopentadiene and 1,3-cyclohexadiene is not diastereoselective, the diastereomers can be separated by HPLC. The cycloadducts from 1,3-cyclohexadiene and vinylsulfoximine 1b have been converted to bicyclo[2.2.2]oct-2-ene and bicyclo-[2.2.2]oct-2-en-5-one.