Scott H. Watterson

Cycloaddition reactions of unsaturated sulfones

The reaction of a series of allyl-substituted bis(phenylsulfony1)- methanes or dimethyl malonates with 2,3-bis(phenylsulfonyl)- l13-butadiene in the presence of base afforded alkenyl-substituted allenes in good yield. The reaction proceeds by initial attack of the soft carbanion onto the terminal position of the diene and subsequent PhS02- elimination to give the phenylsulfonyl sub- stituted allene. The thermal reactions of these phenylsulfonyl allenes gave (2+2)-cycloadducts. Only the Cl-C2 double bond of the alleneparticipates in the (2+2)-cycloaddition. Stepwise bonding prefers to occur in a 1 ,&ex0 manner rather than in a 1,7-endo fashion. The formation of all products can be rationalized by a mechanism which includes an initial carbon-carbon bond formation involving the central allene carbon to give a diradical intermediate. The product distribution is then determined by the substitution pattern of the alkene and the fate of the diradical intermediate.

ALKYLATION REACTIONS OF 3-(PHENYLSULFONYL)METHYL SUBSTITUTED CYCLOPENTENONES

Abstract The readily available 2,3-dibromo-1-(phenylsulfonyl)-1-propene (DBP) undergoes facile reaction with several 1,3-dicarbonyl compounds under basic conditions to give (phenylsulfonyl)methyl substituted cyclopentenones. The pendant sulfonyl group at the C3 position of the cyclopentenone ring offers a versatile site for further elaboration via alkylation. These cyclic α-enone systems are easily metallated with sodium hydride, and the resultant carbanion undergoes both bimolecular and intramolecular alkylations. The overall sequence provides a simple and efficient route to functionalized cyclopentenones. The alkylated sulfones were easily desulfonylated upon heating with tri n-butyltin hydride and AIBN in toluene at 110 °C. A novel base-induced transformation was observed using 3-(phenylsulfonyl)methyl-2-(4-iodobutyl)cyclopentenone. Treatment of this compound with one equivalent of NaH in the presence of HMPA afforded 4-methylene-spiro[4.4]non-2-en-1-one. This reaction proceeds by initial γ-alkylation followed by a 1,3-hydrogen shift and subsequent 1,4-elimination of sulfinate anion.

Periselectivity in the base-catalyzed intramolecular [2+2]-cycloaddition reaction of 3-phenylsulfonyl-substituted propynes

Abstract Phenylsulfonyl-substituted allenes containing a tethered π -bond are conveniently prepared reagents that can serve as substrates for intramolecular [2+2]-cycloaddition chemistry.