Sulfonyl chlorides, reductive cleavage

Thiophenethiols are prepared by reduction of the sulfonyl chlorides or, more conveniently, by the reaction of Grignard rea-gents or thienyllithium compounds with sulfur. They have also been obtained by cleavage or thienyl alkyl sulfides with sodium in liquid ammonia. 3-Thiophenethiol is a by-product in the commercial thiophene synthesis. Thiophenethiols have recently also been prepared by a synthesis involving Friedel-Crafts reaction of 2,4-dinitrobenzenesulfenyl chloride with thiophenes, followed by basic cleavage of the resulting sulfide. ... 

Reduction is a possible reaction of almost all sulfur-containing organic compounds. According to the conditions used it leads either to thiols or to disulfides. For these purposes importance attaches primarily to reduction of aromatic sulfonyl chlorides and hydrogenating cleavage of disulfides. 

Isomannide (80) was the core for a hexahydrofurofuran library." Primary amines were loaded onto solid-support by reductive amination and acylated with bromoacetic acid to give bromides 79 (Scheme 7.16). Alkylation of bromides 79 on solid-support with isomannide (80) gave the solid-supported alcohols 81. A Mitsunobu reaction with phthalimide (82) proceeded to furnish amines 83 in excellent yield and purity after removal of the protecting group." " Support-bound primary amines 83 were converted to secondary amines by stepwise imine formation with aldehydes 84 and reduction with sodium borohydride." The hindered secondary amines 85 were acylated with acid chlorides, sulfonyl chlorides, isocyanates, and isothiocyanates to yield 87 after cleavage from solid-support. 

The reductive desulfonylation of a-sulfonyl esters with tin hydrides only succeeds with n-deficient heterocyclic sulfones (Eq. 104).175 These sulfones are inert under standard procedures using Al/Hg or Na/Hg, but undergo facile C-S cleavage with tin hydrides. Substitution of //-liu3Snl) for n-Bu3SnH gives access to a-deuterated esters.58 A catalytic version of the reaction is carried out with substoichiometric amounts of tributyltin chloride and an excess of poly(methyl-hydrosiloxane) (PMHS) in the presence of potassium fluoride. This method has been employed for the synthesis of 2-fluoroalkanoates (Eq. 105).58... 

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