Sulphonyl transfer, mechanisms

Doubt has been cast on whether the acylation and sulphonylation of sulphamic esters (Table 5.22) proceeds via a phase-transfer mechanism. The rates of the reactions are enhanced and the reproducibility is increased by the addition of a catalyst, but yields in excess of 75% can be readily attained over an extended reaction time in the absence of the catalyst [46]. 

Several compounds have been prepared by nucleophilic substitution of chlorine in 2-chloro-l,3-dithian with Grignard reagent (RMgBr), malonic esters, and phenols.A mechanism for the de-ethoxycarbonylation of the 2-(l,3-dithianyl)malonates by sodium chloride or sodium ethoxide has been studied. 2-Chlorotetrahydrofuran reacts with nucleophiles such as 2-lithio-2-phenyl-l,3-dithian (326) by three simultaneous mechanisms i.e. substitution, proton abstraction, and electron transfer) to give the products (327)—(330) (Scheme 12)/° When a dithian (331 R = H or COiMe) was treated with a sulphonyl chloride in pyridine, ring-expansion to the 5//-l,4-dithiepin (332) occurred instead of the expected formation of a sulphonate. ... 

Radical Addition. Free-radical addition of toluene-/>-sulphonyl iodide or methanesulphonyl iodide to acetylenes proceeds readily and stereoselectively when the two are mixed in ether and illuminated. The high yields of crystalline products (102) obtained imply that in the mechanism (Scheme 7), chain transfer by the sulphonyl iodide ( 3) is much faster than isomerization of the intermediate vinyl radical (k. The /ra 5-addition was confirmed by zinc-acetic acid reduction to the sulphone, and by Z-ray analysis of one of the adducts. 

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