Additions of Organocopper Reagents and Heteroatom Nucleophiles to 1-Phenylseleno-2-( p -toluenesulfonyl)ethyne. Preparation of Vinyl and Allenic Sulfones and Formation of Michael, Anti-Michael, and Rearrangement Products

1-Phenylseleno-2-( p -toluenesulfonyl)ethyne ( 4 ) was produced nearly quantitatively from p -(toluenesulfonyl)ethyne and benzeneselenenyl chloride. It underwent stereo- and regioselective syn-additions of organocopper reagents RCu(CN)Li to the β-position of the sulfone moiety to afford adducts 5 . Further reaction of the products with reagents RCu(SePh)Li resulted in substitution of the phenylseleno group with retention of configuration. Control of E, Z -stereochemistry in the product β,β-disubstituted vinyl sulfones is therefore achieved by the order of addition of the reagents. Selenoxide syn-elimination of adducts 5 afforded the corresponding allenic sulfones. The additions of amines and alkoxides to 4 produced the corresponding anti-Michael regioisomers (where attack occurred α to the sulfone group) as the major or sole products. The additions were highly stereoselective, proceeding by anti-addition in the anti-Michael series and by syn-addition in the corresponding Michael regioisomers. The reactions of 4 with thiolates and selenolates were more complex, affording rearranged adducts and Michael adducts as the major and minor products, respectively. The formation of the rearranged products can be rationalized by a series of addition−elimination processes. Phenylselenoethyne ( 43 ) underwent conjugate additions of pyrrolidine, sodium methoxide, sodium ethanethiolate, and benzeneselenolate anion, affording the corresponding cis isomers via anti-addition. The experiments with heteroatom nucleophiles and acetylenes 4 and 43 show that the phenylseleno group has a surprisingly large activating effect upon conjugate additions.