2-Phenylthio-1 -alkenes

Various 1,2-bifunctionalized alkenes containing heteroatoms are prepared by addition to alkynes. Thiophosphorylation of 1-octyne with phosphorothiolate 131 provided (Z)-l-(diphenoxyphosphinyl)-2-(phenylthio)-l-octene in good yield [40]. A useful synthetic method for (Z)-3-phenylthioacrylate derivative is the Pd-catalyzed thioesterification of 1-alkynes with 6)-methyl S-phenyl thiocarbonate (132). Addition of 132 to 1-octyne using Pd(PCy3)2 as a catalyst afforded methyl (Z)-3-phenylthio-2-nonenoate in 86% yield [41]. (Z)-l,2-Bis(phenylthio)alkene was prepared in good yield by stereoselective Pd-catalyzed addition of (PhS)2 (3) to 1-alkyne [2]. 

Formation of l,3-Bis(phenylthio)alkenes from Aldehydes and Ketones. a nsaturated aldehydes and ketones form 1,3-bis(phenylthio)alkenes on treatment with phenyl thioborate (eq 3). The (phenylthio)alkenes are ) -acyl vinyl anion equivalents (eq 4). 

Michael addition of nucleophiles to the nitro-(phenylthio)alkene (61) provided, after ozonolysis of the intermediate nitronates, substituted phenylthiol esters (62) with good to excellent diastereoselectivity. They were converted to derivatives (63) of methyl L-alluronate by treatment with methanolic mercury(II) acetate. ... 

Only one previous method exists for the replacement of a -hydrogen atom of a conjugated enone by an electrophilic substituent. Now treatment of aj8-unsaturated aldehydes and ketones with triphenylthioborate has been shown to provide 1,3-bis(phenylthio)alkene derivatives, the anions of which are effective /S-acyl vinyl anion equivalents (Scheme 51). ... 

Han L, Tanaka M. Novel palladium-catalyzed thiophosphor-ylation of alkynes with phosphoiothioate an efficient route to ( -l-(diphenoxyphosphinyl)-2-(phenylthio)alkenes. Chem. Lett. 1999 863 64. 

The thioboration of terminal alkynes with 9-(alkylthio)-9-borabicyclo[3.3.1]-nonanes (9-RS-9-BBN) proceeds regio- and stereoselectively by catalysis of Pd(Ph,P)4 to produce the 9-[(Z)-2-(alkylthio)-l-alkeny)]-9-BBN derivative 667 in high yields. The protonation of the product 667 with MeOH affords the Markownikov adduct 668 of thiol to 1-alkyne. One-pot synthesis of alkenyl sulfide derivatives 669 via the Pd-catalyzed thioboration-cross-coupling sequence is also possible. Another preparative method for alkenyl sulfides is the Pd-catalyzed cross-coupling of 9-alkyl-9-BBN with l-bromo-l-phe-nylthioethene or 2-bromo-l-phenylthio-l-alkene[534]. 

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. 

Finally, with the aim of discovering novel chiral oxomolybdenum catalysts able to perform enantioselective alkene epoxidations, Kuhn et al. have reported the exploration of the catalytic behaviour of a series of dioxomolybdenum(VI) complexes with chiral cw-8-phenylthiomenthol ligands derived from ( + )-pulegone. Therefore, the epoxidation of c -p-methylstyrene using t-butyl-hydroperoxide as the oxidant and performed in the presence of ( + )-(2i ,5i )-2-[1-methyl-l-(phenylthio)ethyl]-5-methylcyclohexanone oxime as the ligand, did not produce, however, a significant optical induction in these conditions. 

The addition of alkoxides to 2-nitro-l-phenylthio-l-alkenes affords P-nitro-aldehyde acetals.276 The reaction of the same nitroalkenes with amines gives nitroenamines.270 They are important intermediates for organic synthesis and are generally prepared by the reaction of nitroalkanes with triethylorthoformate in the presence of alcohols or secondary amines.2"1 0 The methods of Eqs. 4.20 and 4.21 have some merits over the conventional methods, for variously substituted (3-nitro-aldehydes acetals or nitroenamines are readily prepared by these methods. 

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. 

Addition of halogens and pseudohalogens to the cyclopropylthiocarbene chromium complexes 122 affords the 1,4-dihalo-1-phenylthio-l-alkenes 123 stereoselectively [65]. Electrophilic halogen is likely to activate the carbene complexes, followed by the homo-Michael addition of halide anion. (Scheme 44)... 

Stereo- and regioselective synthesis of trienes and tetraenes has been reported by palladium-catalysed coupling of (E)- or (Z)-l-alkenyl boronates with (E)- or (Z)-2-bromo-1-phenylthio-l-alkenes followed by treatment with a Grignard reagent in the presence of a nickel catalyst (equation 146)259. 

Regio- and stereoselective addition of 9-(phenylthio)-9-BBN to terminal alkynes is catalyzed by Pd(PPh3)4 to produce 9-[(Z)-/ -(phenylthio)alkyenyl]-9-BBN (Scheme 73) 283 Addition of styrene avoids catalyst deactivation by trapping free thiophenol generated in the reaction mixture. The produced alkenylboranes exhibit high reactivities for protonolysis with MeOH to produce 2-phenylthio-l-alkenes. 

Radical [3 + 2 cycloaddition. Cyclopentanes can be prepared by addition of alkenes across vinylcyclopropanes catalyzed by phenylthio radicals formed from (C6H5S)2 and AIBN. A Lewis acid such as A1(CH3)3 can increase the rate and the stereoselectivity of this radical initiated cycloaddition. Thus the combination of the vinylcyclopropyl ester 1 with f-butyl acrylate (2) provides the four possible cyclo-... 

Chloro(phenylthio)carbene [32] has been produced by the standard phase-transfer catalytic procedure from PhSCHCK and trapped by alkenes (see Section 7.3), although the carbene is also prone to dimerization to give [PhS(Cl)C=C(Cl)SPhj. In a similar manner, phenylthiocarbene has been obtained from PhSCH2Cl [33] and chloro(phenoxy)carbene from dichloro(phenoxy)methane [34]. Reaction of the analogous seleno derivatives produce the conesponding phenylselenocarbenes... 

Phenylthiocarbene, chloro(phenylthio)carbene, their seleno analogues, and the less electrophilic chloro(methylthio)carbene react with a range of alkenes [145-148], as does chloro(phenoxy)carbene [149]. 

Among the electron-rich alkenes, vinylsulfides are especially amenable to cation-radical reduction an important feature is the absence of hydrogenolysis of carbon-sulfur bonds. The reduction of [(phenylthio)methylene]cyclohexane is efficient (88%), and the retention of the phenylthio group clearly contrasts with catalytic hydrogenation (Mirafzal et al. 1993). This provides versatile functionality for further synthetic operations. 

An efficient process for one-carbon homologation to aldehydes is based on cyclic boronate esters.17 These can be prepared by hydroboration of an alkene with dibromobor-ane, followed by conversion of the dibromoborane to the cyclic ester. The homologation step is carried out by addition of methoxy(phenylthio)methyllithium to the boronate ester. The migration step is induced by mercuric ion. Use of enantioenriched boranes and boronates leads to products containing the groups of retained configuration.18... 

Generell sind auch (jE )-2-Nitro-1-phenylthio-l-alkene einsetzbar, die unter Abspaltung der Phenylthio-Funktion zu l,1-Dialkoxy-2-nitro-alkanen (77-78%)4reagieren ... 

The synthetic utility of a-phosphorus- and a-thio-stabilized carbanions is the subject of numerous reviews.21 Notable are additions of phosphonium ylides (237),183 sulfonium ylides (238),l84 ° oxosulfo-nium ylides (239)184 " and sulfoximine ylides (240)184,1 to electron-deficient alkenes which afford nucleophilic cyclopropanation products. In contrast, with a-(phenylthio)-stabilized carbanions, which are not acyl anion equivalents, either nucleophilic cyclopropanation or retention of the hetero substituent occurs, depending on the acceptor and reaction conditions used. For example, carbanion (241) adds to 1,1-... 

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