Episulfonium ions synthesis

Sulfenocycloamination. Treatment of an w-alkenylamine hydrochloride with C H SCI gives a mixture of two adducts that undergoes ring closure via an episulfonium ion to a single cyclic amine on treatment with base (K,CO,)- The reaction is useful for synthesis of pyrrolidines and piperidines (equation I) and pyrrolizidines (equation 11). 

The deoxynucleoside problem was approached from another sequence, in which 3,5-di-O-benzoyl-D-arabinofuranosyl chloride was prepared, and then treated with sodium ethanethioxide to give, in a stereoselective reaction, ethyl 3,5-di-O-benzoyl-l-thio-a-D-arabinofuranoside, a thiogly-coside having the proper structure for neighboring-group transfer of the ethylthio group to C-2 by way of an episulfonium ion intermediate. This approach was later expanded in a successful synthesis of 2 -S-methyl-2 -thioadenosine and other derivatives of 2 -thioadenosine, all of which were potential precursors to 2 -deoxyadenosine. 

The key-step in the synthesis of the 4-thio-oc,P-D-ery/Aro-pentofuranose derivative 31 from L-arabinose was the well-established ring-closure 29 ->30 (see Vol. 29, Chapter 11, Ref. 14). A range of other 2-deoxy-D-ery/Aro-pentose dibenzyl-dithioacetals have been prepared and similarly cyclized to 2-deoxy-4-thio-D-eryt/jro-pentofuranose derivatives. A synthesis of 4-thio-l,4-anhydro-L-ribitol (32) from D-arabinitoI was based on the episulfonium ion rearrangement shown in Scheme The conformation of 4-thio-L-lyxono-1,4-lactone is referred to in Chapter 21. 

For cyclizations via epoxide opening leading to C-glycosides and related compounds, see [2,204-206]. For the synthesis of C-glycosides and related compounds by episelenonium-mediated cyclizations, see [2, 207]. For episulfonium ion promoted cyclizations of hydroxy alkenes, see [2]. For the preparation of C-glycosides... 

Among a variety of possible glycal-based three-membered cyclic intermediates, only glycal epoxides and 1,2-episulfonium ions have been employed in the synthesis of C-glycosides and related compounds. 

Johnston BD, Pinto BM (2000) Synthesis of thio-linked disaccharides by 1 — 2 intramolecular thioglycosyl migration oxocarbenium versus episulfonium ion intermediates. J Org Chem 65 4607 17... 

Hairing SR, Edstrom ED, Livinghouse T (1992) Episulfonium ions and episelenonium ions. Versatile heterocyclic cations for the synthesis of natural products. Adv Heterocycl Nat Prod Synth 2 299-376... 

We have previously reported on the excellent properties of the mustard-type sulfur compound 12 (Fig. 11.3) as a scaffold for the synthesis of functional molecules. The nucleophilic displacement of the chlorides in 12 occurs in high efficiency with a variety of nucleophiles using on water conditions. These reactions occur via episulfonium ion intermediates, and are therefore uniquely assisted by the aqueous medium. ... 

Edstrom ED, Livinghouse T. New methods for the generation of episulfonium ions. An application to the synthesis of carbocycles via sulfenium ion promoted arene-alkene cycli-zations./. Am. Chem. Soc. 1986 108 1334-1336. 

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