Homoallyl sulfides

Homoallyl ethers or sulfides.1 gem-Methoxy(phenylthio)alkanes (2), prepared by reaction of 1 with alkyl halides, react with allyltributyltin compounds in the presence of a Lewis acid to form either homoallyl methyl ethers or homoallyl phenyl sulfides. Use of BF3 etherate results in selective cleavage of the phenylthio group to provide homoallyl ethers, whereas TiCl effects cleavage of the methoxy group with formation of homoallyl sulfides. 

The pioneering work on thia-[2,3]-Wittig rearrangement was reported by Rautenstrauch in 1971 °. The reaction of allyl sulfides 137 with n-BuLi at —30°C for 1.5-4 h gave homoallyl sulfide or thiol 138 ([2,3]-product) exclusively (equation 81). In contrast, a similar reaction of vinyl sulfide 139 gave no [1,2]-rearrangement product 141 albeit a-thio-carbanion was generated as shown by its methylation to 140 (equation 82) °. 

Unsaturated 1,5-dicarbonyl compounds. The phenylthioalkylation of silyl enol ethers of carbonyl compounds (9, 521-522) can be extended to the synthesis of unsaturated 1,5-dicarbonyl compounds. In a typical reaction the enol silyl ether of a ketone is alkylated with the unsaturated chloride 1 under ZnBr2 catalysis to give a homoallyl sulfide. Ozonolysis of the methylene group is accompanied by oxidation of the phenylthio group sulfoxide elimination results in an unsaturated 1,5-aldehydo ketone (equation I). Alkylation with 2 results in a methyl ketone (equation II). 

Phosphorus-functionalized homoallyl sulfides have been prepared using either base-promoted yUde generation [ 196] or, more recently, the carbenoid route (Scheme 84) [197]. When diazomethylphosphonate 341 [198] was reacted with allyhc sulfides 342, the rearranged a-phosphorylated sulfides 344... 

One of the first examples of an excellent stereoselectivity in open-chain allylic sulfides was published in 1986 by Weinreb [208]. In this remarkable paper a diastereoselective Diels-Alder reaction of a sulfinyl dienophile with a substituted diene delivered cycloadducts as described earlier (Sect. 3.5.3, Scheme 59). After ring opening and reduction Z-olefin 362 was produced which, after S-methylation and base treatment rearranged to isomerically pure homoallyl sulfide 363. 

Complex 376 can be prepared from enantiomerically pure rhenium precursor 381. The former can be deprotonated at low temperatures initiating the [2,3]-sigmatropic rearrangement to diastereomerically pure homoallylic sulfide complex 377. After S-alkylation, cyanide treatment releases the S ligand as product 379. As an extension of this work the authors showed that iron and ruthenium complexes can be used, too [219]. 

Thiazol-2-yl allyl sulfides react with organomagnesium compounds in the presence of CuBr to afford optically active alkenes in good yields and selectivities <1996T10799>. Thiazole and benzothiazole allyl sulfides have been shown to react with excess ethyl diazoacetate in the presence of a copper(i) hexafluorophosphate acetonitrile complex to give, via formation of the resultant homoallylic sulfide intermediates, conjugated dienoic esters in good yields <1997TL3289>. /3-Ketosulfides of benzothiazole 143 are very prone to deprotonation by weak bases. Treatment... 

Cohen has used a soluble version of the Simmons-Smith reagent to promote the 3,2-rearrangement of allylic sulfides (Scheme 52). He has also applied this methodology to the synthesis of sarkomycin (225). The allylic sulfide (221), easily available via a Petrow reaction, was first alkylated and the sulfo-nium ylide was then generated by a fluoride-promoted desilylation. Rearrangement of the ylide (223) gave the homoallylic sulfide (224) which was eventually transformed into sarkomycin (Scheme 53). 

Alkylated thioaldehydes, generated by Pummerer reanangements or treatment of a-chloro sulfides with SnCU, undergo ene type reactions with terminal alkenes to give homoallylic sulfides in 50-70% yield (equation 20). ... 

Another example is the synthesis of (—)-deoxocassine (2) reported by Raghavan and coworkers [35]. The reaction between silyl ether 109 and Burgesssalt afforded corresponding sulfilimine. Deprotection of the TBS group with TBAF followed by reaction with NBS and subsequent protection with DMP afforded acetonide 110. Subjection to a one-pot Pummerer rearrangement followed by ene reaction afforded the homoallylic sulfide. Debromination... 

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