α-Oxosulfines: reactions with alkenes and alkynes

Abstract

Thiochroman-4-one 1,1-dioxide has been successfully converted into 3-sulfinylthiochroman-4-one 1,1-dioxide and the reactions of this α-oxosulfine with a series of alkenes have been carefully investigated. The α-oxosulfine was found to react as a Diels–Alder diene with 2-methylpropene, Z- and E-2-butene, 2-ethyl-1-butene, 1-pentene, Z-2-pentene, and cyclopentene and cyclohexene to produce a new group of heterocyclic compounds, the 2,3-dihydro-5H-1,4-oxathiino[3,2-c][1]benzothiopyrans, in yields ranging from 21 to 42%. In all cases, formation of the Diels–Alder adduct was accompanied by a second type of product, identified as the product of electrophilic addition (EA) of a sulfenium species to the alkene, in lesser yields, ranging from 9 to 18%. When the trapping dienophile used was 3,3-dimethyl-1-butene, only the EA adduct was obtained, in 28% yield. Formation of only the EA type of adduct was also observed in reactions of the α-oxosulfine with 2-butyne (21%) and with the thione 2,2,4,4-tetramethylpentane-3-thione (di-tert-butyl thioketone) (16%). Attempts to prepare the α-oxosulfines corresponding to the following ketones are also described: thiochroman-4-one 1-oxide, isothiochromanone and isothiochromanone 2,2-dioxide, tetrahydrothiophen-3-one 1,1-dioxide, 3,3,5,5-tetramethylcyclohexanone, and 2-indanone. Keywords: Diels–Alder, electrophilic addition, sulfenic acid.