Diels-Alder Cycloadditions of Ethyl 2-Carbomethoxyethenesulfinates with Cyclopentadiene. Lewis Acid Enhancement and Adduct Identification with the Assistance of Competitive Stereodifferentiating Iodolactonization and Iodosultinization Reactions.
Ethyl (Z)-2-carbomethoxyethenesulfinate (1) and ethyl (E)-2-carbomethoxyethenesulfinate (2) were each subjected to cyclopentadiene (ca. 3 equiv) in order to determine their reactivity in Diels-Alder reactions. Thermal reactions proceeded in less than 4 h, while Lewis Acid enhanced reactions were substantially faster and demonstrated greater selectivity. In particular, the BF(3).Et(2)O-mediated cycloaddition of 1 gave syn/endo cycloadduct 3a as a major diastereomer in about 90% yield. The reactions of 2 were less synthetically useful. The structures of the cycloadducts were established through a combination of X-ray crystal structure determinations and through exposure of the compounds to an electrophilic iodine reagent. Each cycloadduct underwent an iodocyclization reaction with either the carboxylic ester or the sulfinate ester participating in the formation of a polycyclic lactone or sultine, respectively. The iodocyclization reactions allowed further elucidation of the cycloadduct structures.
Lear
Yvonne
Y
Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, Department of Chemistry and Biochemistry, University of Guelph, Guelph, ON, Canada, N1G 2W1.
Schwan
Adrian L.
AL