ALKYLATION REACTIONS OF 3-(PHENYLSULFONYL)METHYL SUBSTITUTED CYCLOPENTENONES

The readily available 2,3-dibromo-1-(phenylsulfonyl)-1-propene (DBP) u ndergoes facile reaction with several 1,3-dicarbonyl compounds under b asic conditions to give (phenylsulfonyl)methyl substituted cyclopenten ones. The pendant sulfonyl group at the C-3 position of the cyclopente none ring offers a versatile site for further elaboration via alkylati on. These cyclic alpha-enone systems are easily metallated with sodium hydride, and the resultant carbanion undergoes both bimolecular and i ntramolecular alkylation reactions. The overall sequence provides a si mple and efficient route to functionalized cyclopentenones. The alkyla ted sulfones were easily desulfonylated upon heating with tri n-butylt in hydride and AIBN in toluene at 110 degrees C. A novel base-induced transformation was observed using enylsulfonyl)methyl-2-(4-iodobutyl)c yclopentenone. Treatment of this compound with one equivalent of NaH i n the presence of HMPA afforded 4-methylene-spiro[4.4]non-2-en-1-one. This reaction proceeds by initial gamma-alkylation followed by a 1,3-h ydrogen shift and subsequent 1,4-elimination of sulfinate anion, (C) 1 998 Published by Elsevier Science Ltd. All rights reserved.