| Abstract: | Glycosylsulfenyl snf (Glycosylthio) sulfenyl Halides (Halogeno and Halogenothio 1-Thioglycosides, Resp.): Preparation and Reaction with Alkenes The disulfides 11–17 and 20 were prepared from 7, 9 , and 18 via the dithiocarbonates 8, 10 , and 19 , respectively (Scheme 2). The structure of 11 and of 13 was established by X-ray analysis. Chlorolysis (SO2Cl2) of 11 gave mostly the sulfenyl chloride 24 , characterized as the sulfenamide 26 , a small amount of 21 , characterized as the (glycosylthio)sulfenamide 23 , and the glycosyl chloride 27 (Scheme 3). Bromolysis of 11 followed by treatment of the crude with PhNH2 yielded only 28 . Chlorolysis of the diglycosyl disulfide 13 , however, gave mostly the (glycosylthio)sulfenyl chloride 21 and 27 , besides 24 . Bromolysis of 13 (→ 22 and traces of 25 ) followed by treatment with PhNH2 gave an even higher proportion of 23 . Similarly, 20 led to 29 and hence to 30 . In solution (CH2Cl2), the sulfenyl chloride 24 decomposes faster than the (thio)sulfenyl chloride 21 , and both interconvert. Addition of crude 24 to styrene (?78°) yielded the chloro-sulfide 31 and some 37 , both in low yields. The product of the addition of 24 to l-methylcyclohexene was transformed into the triol 32 . Silyl ethers of allylic alcohols reacted with 24 only at room temperature, yielding, after desilylation, isomer mixtures 33 and 34 , and pure 35 . Much higher yields were achieved for the addition of (thio)sulfenyl halides yielding halogeno-disulfides. Good diastereoselctivites were only obtained with 21 , its cyclohexylidene-protected analogue, and 22 , and this only in the addition to styrene (→ 36, 37, 38 ), to (E)-disubstituted alkenes (→ 46, 48, 49a/b, 50a/b, 53 ), and to trisubstituted alkenes (→ 47, 51, 52, 54, 55 ). Other monosubstituted alkenes (→ 41–45 ) and (Z)-hex-2-ene (→ 49c/d,50c/d ) reacted with low diastereoselectivities. Where structurally possible, a stereospecific trans-addition was observed; regioselectivity was observed in the addition to mono- and trisubstituted alkenes and to derivatives of allyl alcohols. The absolute configuration of the 2-chloro-disulfides was either established by X-ray analysis ( 47a ) or determined by transforming (LiAlH4) the chloro-disulfides into known thiiranes (Scheme 5). Thus, 37, 48 , and the mixture of 49a/b and 50a/b gave the thiiranes 56, 61 , and 64 , respectively, in good-to-acceptable yields (Scheme 5). Harsher conditions transformed 56 into the thiols 57 and 58 . Similarly, 61 gave 62 . The enantiomeric excesses of these thiols were determined by GC analysis of their esters obtained with (?)-camphanoyl chloride. Addition of 21 to {(E)-hex-2-enyl]oxy}trimethylsilane, followed by LiAlH4 reduction and desilylation, gave the known 66 (63%, e.e. 74%). The diastereoselectivity of the addition of 21 to trans-disubstituted and trisubstituted alkenes is rationalized by assuming a preferred conformation of the (thio)sulfenyl chloride and destabilizing steric interactions with one of the alkene substituents, while the diastereoselectivity of the addition to styrene is explained by postulating a stabilizing interaction between the phenyl ring and the C(1)–S substituent (Fig.4). |
