Feasibility of sigmatropic rearrangement on electron-deficient coumarinyl ketones

Abstract

Different alkyl/aryl 7-hydroxy-8-coumarinyl ketones were converted to 7-O-allyl and 7-O-cyclohexenyl ethers and the study of hitherto unreported sigmatropic rearrangement on 7-O-allyl and 7-O-cyclohex-2'-ene-1'-ylcoumarinyl ketones prepared is accounted herein. The rearrangement yielded alkyl/aryl 6-allyl-7-hydroxy-8-coumarinyl ketones 3 and alkyl/aryl 6-cyclohex-2'-en-1'-yl-7-hydroxy-8-coumarinyl ketones 7 as the major products. Interestingly, unusual selectivity was observed in the case of alkyl 7-O-allylcoumarinyl ketones. Thus alkyl 3-allyl-7-hydroxy-8-coumarinyl ketones 4 and alkyl 8-allyl-7-hydroxy-6-coumarinyl ketones 5 were the outcome from alkyl 7-O-allyl-8-coumarinyl ketones and alkyl 4-methyl-7-O-allyl-8-coumarinyl ketones, respectively, albeit in minor yields.Key words: allyloxycoumarinyl ketones, 7-O-cyclohex-2'-en-1'-ylcoumarinyl ketones, sigmatropic rearrangement, 3-allylcoumarinyl ketones, 8-allylcoumarinyl ketones.