Reactivity and utility of allenylphosphonates: Formation of a novel hydroperoxide and propargylic alcohol and facile thiol addition under catalyst-free, solvent-free conditions

Abstract

2-(Propa-1,2-dienyl)-, 2-(buta-1,2-dienyl)-, and 2-(3-methylbuta-1,2- dienyl)-substituted 5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxides 1a-c react readily upon heating with thiols under catalyst-free, base-free, and solvent-free conditions to give sulfanyl-substituted phosphonates. The reaction undergoes to essential completion within 15 minutes under microwave radiation. While 1a,b react with 4-chlorothiophenol to afford both 2-[2-(4- chlorophenylsulfanyl)prop-1-enyl]- 12 and 2-[2-(4-chlorophenylsulfanyl)prop-2- enyl]-5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxides 13, 1c gives 2-[2-(4-chlorophenylsulfanyl)-3-methylbut-2-enyl]-5,5-dimethyl-1,3, 2-dioxaphosphinane 2-oxide (13d) regioselectively. Molecular oxygen undergoes a novel reaction with the allene 1c to give propargylic alcohol 2-(3-hydroxy-3-methylbut-1-ynyl)-5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide (16) via the corresponding hydroperoxide; the structures of these were confirmed by X-ray crystallography. The synthetic utility of the sulfanyl-substituted allyphosphonate 13d in the Horner-Wadsworth-Emmons reaction to afford synthetically valuable sulfanyl-substituted buta-1,3-dienes and a conjugated triene is demonstrated. © Georg Thieme Verlag Stuttgart.