Reaction of arylsulfonylhydrazones of aldehydes with alpha-magnesio sulfones. A novel olefin synthesis

Reactions of representative tosylhydrazones of aldehydes and ketones with a -metalated sulfones were examined in order to develop a practical olefinati on method. Treatment of aldehyde tosylhydrazone 2 with an excess of alpha - lithiated methyl phenyl or dimethyl sulfones yielded 3a. The reaction of 2 with sterically unhindered lithiated alkyl sulfones gave mixtures of the re spective olefination products 3b-d along with the Shapiro fragmentation pro duct 4. Sterically hindered lithiated sulfones afforded Shapiro products ex clusively. In contrast, aldehyde tosylhydrazones 2 or 6 in reactions with a variety of alpha -magnesio primary or secondary alkyl sulfones gave olefin ation products 3a-j and 7a-c in high yields (Tables 1 and 2). beta -Branche d alkyl sulfones afforded predominantly (E)-alkenes, whereas unhindered pri mary sulfones gave mixtures of (E)- and (Z)-alkenes with low selectivity. R eaction of the 2,4,6-triisopropylbenzenesulfonylhydrazone (trisylhydrazone) of cyclodecanone 11c with alpha -magnesio methyl phenyl sulfone afforded t he methylidene derivative 12a contaminated with the Shapiro product 13. Tos ylhydrazone 2 resisted reaction with i-PrMgCl and gave only a small amount of the addition product in reaction with Bu2Mg. Some mechanistic aspects of the reaction of tosylhydrazones with organomagnesium compounds are discuss ed.