Benzenesulfenyl chloride reactions with alkenes

Another useful cyclization results in the stereoselective synthesis of -lactams from thiiranium ions derived from a, -unsaturated amides. Unsaturamd amides are treated with benzenesulfenyl chloride and the product is subsequently treated with base under phase transfer conditions. The reaction legeiMiates a thiiranium ion in the presence of amide anion, which then tyclizes to form -lactams. The regiochemistry of the alkene aMtion determines the eventual stereochemical outcome e.g. cis alkenes produce c(5- -lactams Scheme 2). The yields of the cyclization products are quite sensitive to the amide-protecting group which was enqtloyed. With 4-anisyl amide the yield is modoate (73%), but wdth 4-nitr henyl amide the yield is excellent (97%), suggesting that the amide must be deprotonated before cyclization can occur. 

Enolates react with sulfenyl halides to give an a-alkylthio ketone. As shown for cyclohexanone, reaction with LDA followed benzenesulfenyl chloride (PhSCl) produced phenylthio derivative 109. The proton adjacent to both the carbonyl and the sulfur (the a-proton) was more acidic and it was deprotonated with potassium hydride, forming the enolate, and alkylation with iodobutane gave a 91% yield of 110. As mentioned in Chapter 2, the sulfide moiety can be oxidized to a sulfoxide and thermally eliminated (syn elimination, sec. 2.9.C.v) to give an alkene. 9 Similar methodology can be applied to selenides, R—Se—R. O... 

Some electrophiles require a separate activation step, as in the stereospecific reaction of alkenes with benzenesulfenyl chloride (eq 15). The intermediate that actually reacts with the aUylsilane is presumably the episulfonium ion. There is a corresponding reaction of epioxonium ions derived from 2-bromoethyl ethers. Intramolecular hydrosilylation of an ester generates an acetal, which reacts with allyltrimethylsilane in the usual way and with high stereocontrol to make an anti 1,3-diol derivative (eq 16). ... 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ ]

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