NaOH-catalyzed thiolysis of α,β-epoxyketones in water.: A key step in the synthesis of target molecules starting from α,β-unsaturated ketones

NaOH (0.02-0.3 molar equiv) is an efficient catalyst for the thiolysis reactions of a,p-epoxy ketones with alkyl and aryl thiols in water. Thiolysis of 3,4-epoxyheptan-2-one (1) with thiols 2a-d has been accomplished in mild conditions (30 degreesC and pH 6 or 9) with complete C-alpha-regioselectivity and anti-stereoselectivity, and the corresponding anti-beta-carbonyl-beta-hydroxysulfides 3a-d have been prepared in excellent yields (95-98%). Compounds 3a-d, depending on their nature and pH conditions, have undergone dehydration, C-3 epimerization reaction, and retroaldol condensation. Dehydration of anti-3a-d has been chemoselectively carried out by in situ acidic treatment at 70 degreesC, giving stereoselectively the related (Z)-vinyl sulfides 4 in 89-94% overall yields. Under NaOH-catalyzed thiolysis conditions, cyclic alpha,beta-epoxyketones 6-9 have shown C-alpha attack only and spontaneously dehydrated to furnish the corresponding vinyl sulfides in high yields (90-96%). The reactions of calchone oxide (10) with thiols 2b-d have exclusively resulted in the formation of beta-carbonylsulfides 10b-d (82-93% yield), coming from the nucleophilic attack at the a-position and retroaldol condensation. To highlight the synthetic utility of this procedure, one-pot multisteps preparation of vinyl sulfides 7b and 7c, vinyl sulfoxides 12 and 13, and 1,5,6,7-tetrahydro-4H-1,2,3-benzotriazol-4-one (14) starting from 2-cyclohexen-1-one (11) have also been reported.