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 qua ntitatively from p-(toluenesulfonyl)ethyne and benzeneselenenyl chlori de. It underwent stereo- and regioselective syn-additions of organocop per reagents RCu(CN)Li to the beta-position of the sulfone moiety to a fford adducts 5. Further reaction of the products with reagents RCu(Se Ph)Li resulted in substitution of the phenylseleno group with retentio n of configuration. Control of E,Z-stereochemistry in the product beta ,beta-disubstituted vinyl sulfones is therefore achieved by the order of addition of the reagents. Selenoxide syn-elimination of adducts 5 a fforded the corresponding allenic sulfones. The additions of amines an d alkoxides to 4 produced the corresponding anti-Michael regioisomers (where attack occurred a to the sulfone group) as the major or sole pr oducts. The additions were highly stereoselective, proceeding by anti- addition in the anti-Michael series and by syn-addition in the corresp onding Michael regioisomers. The reactions of 4 with thiolates and sel enolates were more complex, affording rearranged adducts and Michael a dducts as the major and minor products, respectively. The formation of the rearranged products can be rationalized by a series of addition-e limination processes. Phenylselenoethyne (43) underwent conjugate addi tions of pyrrolidine, sodium methoxide, sodium ethanethiolate, and ben zeneselenolate 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 ac tivating effect upon conjugate additions.