Alcohol From allylic sulfide

We can illustrate the synthesis of allylic alcohols from allylic sulfoxides with this synthesis of the natural product nuciferal. We mentioned this route on p. 1257 because it makes use of a heterocyclic allyl sulfide to introduce an alkyl substituent regioselectively. The allyl sulfide is oxidized to the sulfoxide, which is converted to the rearranged allylic alcohol with diethylamine as the thiophile. Nuciferal is obtained by oxidizing the allylic alcohol to an aldehyde with manganese dioxide. 

Allyltitanocenes are also derived from allyl sulfides, CpjTiClj, and BuLi, and they react with aldehydes to form homoallylic alcohols. 

Efficient procedures for the direct preparation of allyl sulfides from allylic alcohols have also been reported [21]. 

The coupling reaction of epoxide 69 with the anion derived from the allyl sulfide 57, a system derived from geraniol, was accomplished in a 99% yield by employing 4 equivalents of the anion (Scheme 13). Protection of the alcohol as the MOM ether (95%), followed by debenzylation and removal of the phenylthio group under Birch conditions (76%) gave diene 70. Vanadium catalyzed oxidation and spontaneous cyclization of 70 imder acidic conditions afforded a diastereomeric mixture of tetraols 71 and 72 in 61% and 14% yields, respectively. 

Two such rearrangements were used in the preparation of the cyclobutanone (21), a key intermediate in a synthesis of grandisol (22 Scheme 12). A similar rearrangement is observed if the alcohol is allylic to the sulfide (equation 26), and the formation of cyclobutanones from 1-thiophenyl-l-vinyl-cyclopropanes is a closely related process. 

Diallyl sulfides. A one-step preparation from allylic alcohols involves BF, catalysis. 

Allylic sulfides. The direct synthesis from allylic alcohols such as geraniol is accomplished with BFi-OEtz and a thiol. 

An interesting example of this type of chemoselective oxidation has been reported with die reagent mixture derived from diisopropyl sulfide and iV-chlorosuccinimide. This reagent will oxidize selective ly a primary alcohol to an aldehyde at 0 C. Surprisingly, this same reagent at -78 C will oxidize selec lively a secondary alcohol to the corresponding ketone (Scheme 2). Allylic and benzylic alcohols are oxidized at both temperatures. 

Pd(0)-catalyzed rearrangements of dithiocarbonates, such as 13, readily available from the corresponding alcohol, CS2, and Mel, proceed under mild conditions with concomitant elimination of offering an interesting route to allyl sulfides 14 (Scheme 10). 

Stereoselective preparation of CEi-allyl alcohols via radical elimination from ruin -y-phenylthio-fi-nkro alcohols has been reported. The requisiteruin -fi-nitro sulfides are prepared by protonadon of nitronates at low temperanire Isee Chapter 4, and subsequent treatment v/ith Bu-vSnH induces and eliminadon to givelE -alkenes selecdvely IseeEq. 7.112. Unfortunately, it is difficult to get the pure syu-fi-nitro sulfides. Treatment of a rruxnire of syu- and ruin -fi-nitrosulfides v/ith Bu- SnH results in formadon of a rruxnire of (Ey and lZ -alkenes. 

Stereoselective preparation of ( )-allyl alcohols via radical elimination from anti-j-phenylthio-P-nitro alcohols has been reported.154 The requisite anti-P-nitro sulfides are prepared by protonation of nitronates at low temperature (see Chapter 4), and subsequent treatment with Bu3SnH induces anti elimination to give (E)-alkenes selectively (see Eq. 7.112). Unfortunately, it is difficult to get the pure yyw-P-nitro sulfides. Treatment of a mixture of syn- and anti-P-nitrosulfides with Bu3SnH results in formation of a mixture of (E)- and (Z)-alkenes. 

The Pd-catalyzed allylic alkylation of sulfinate ions, thiols, and thiocarboxylate ions with racemic cyclic and acyclic allylic esters in the presence of bisphosphane BPA generally provides for an efficient asymmetric synthesis of allylic sulfones, sulfides, and thioesters. The Pd-catalyzed rearrangements of allylic sulfinates and allylic O-thiocarbamates, both of which proceed very efficiently in the presence of BPA, are attractive alternative ways to the asymmetric synthesis of allylic sulfones and allyUc thioesters also starting from the corresponding racemic alcohols. 

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