Triethyl phosphite sulfides

The photolysis of carboxylic acids and derivatives as lactones, esters and anhydrides can yield decarboxylated products 253>. This reaction has been utilized in the synthesis of a-lactones from cyclic diacyl peroxides 254) (2.34) and in the synthesis of [2,2]paracyclophane by bis-decarboxylation of a lactone precursor (2.35) 255). This latter product was also obtained by photoinduced desulfurization of the analogous cyclic sulfide in the presence of triethyl phosphite 256). 

Bromomethyl acetyl sulfide (26.8 g, 0.16 mol) and triethyl phosphite (28.4 g, 0.17 mol) were combined in a flask fitted with a Dean-Stark trap. The mixture was stirred at 130°C for 2.5 h, during which time ethyl bromide collected in the Dean-Stark trap. The reaction mixture was vacuum distilled to give the pure (diethyl phosphonomethyl) acetyl sulfide (23.5 g, 65%) as a clear oil of bp 105 to 106°C/0.03 torr, which exhibited NMR spectra in accord with the proposed structure. 

Of trialkyl phosphites the most frequently used is triethyl phosphite (EtO)3P (M.W. 166.16, b.p. 156°, density 0.969) which combines with sulfur in thiiranes [291, 294] and gives alkenes in respectable yields. In addition, it can extrude sulfur from sulfides [295], convert a-diketones to acyloins [296], convert a-keto acids to a-hydroxy acids [297], and reduce nitroso compounds to hydroxylamines [298] Procedure 47, p. 111). 

Tertiary and aromatic nitroso compounds are not readily accessible consequently not many reductions have been tried. Nitrosobenzene was converted to azobenzene by lithium aluminum hydride (yield 69%) [592], and o-nitrosobiphenyl to carbazole, probably via a hydroxylamino intermediate, by treatment with triphenylphosphine or triethyl phosphite (yields 69% and 76%, respectively) [298]. Nitrosothymol was transformed to amino-thymol with ammonium sulfide (yield 73-80%) [245], and a-nitroso-/J-naphthol to a-amino-/J-naphthol with sodium hydrosulfite (yield 66-74%) [255]. 

Aliphatic and aromatic sulfides undergo desulfurization with Raney nickel [673], with nickel boride [673], with lithium aluminum hydride in the presence of cupric chloride [675], with titanium dichloride [676], and with triethyl phosphite [677]. In saccharides benzylthioethers were not desulfurized but reduced to toluene and mercaptodeoxysugars using sodium in liquid ammonia [678]. This reduction has general application and replaces catalytic hydrogenolysis, which cannot be used [637]. 

Cyclic sulfides treated with triethyl phosphite eject sulfur and form a new ring less one member [577], From compounds containing sulfur in three-membered rings (thiiranes) alkenes are formed in high yields [291, 294. The same reaction can be achieved with triphenyl phosphine [291]. 

Deoxygenation of the diaryl sulfide (56) with triethyl phosphite gives the phenothiazine (58) in good yield via formation and rearrangement of the spiro intermediate (57). 

Among the more recent approaches to phenoxazines and phenothiazines the reductive cyclization of 2-nitrodiphenyl ethers and sulfides with trialkyl phosphites is the most interesting. Here too a spiro intermediate is involved, produced by attack of an initially formed aryl nitrene on the second aromatic ring. The sulfide (252), for example, reacts with triethyl phosphite to yield 1-methylphenothiazine (253) and it is clear that in this case ring opening of the spiro intermediate also proceeds with a rearrangement of the Smiles type (Scheme 113) (75JCS(P1)2396). 

The photoinduced desulfurization of macrocyclic sulfides in the presence of triethyl phosphite has been widely used in the synthesis of cyclophanes. The [2.2](l,3)-azulenophane (302), for example, has been prepared in this way from the 2,13-dithia[3.3]azulenophane (303).245 Numerous other... 

To a single-necked, round-bottomed flask (100 mL), add 4-chlorophenyl 2-nitrophenyl sulfide 15 (2.0 g, 7.5 mmol), freshly distilled cumene (75 mL), dry triethyl phosphite (5.0 g, 30 mmol) and a magnetic stirrer bar. 

Cadogan et al. performed a reductive cyclization of o-nitro-diphenyl sulfide (14) to phenothiazines (9) using triethyl phosphite. In the case of unsubstituted phenothiazine, the yield was 54%. 

Alkenes. Titanocene bis(triethyl phosphite), which is prepared in situ from titanocene dichloride, triethylphosphite, and Mg, promotes carbonyl olefmation with gem-dichlorides and dithioacetals [e.g., l,l-bis(phenylthio)cyclobutane ] including those derived from enals (to give 1,3-dienes). Enol ethers-and alkenyl sulfides are obtained in the analogous reaction with dithioorthoformates and trithioorthoformates. Cross-coupling of dithioacetal and thiolesters furnishes predominantly (Z)-alkenyl sulfides. ... 

The sulfide 92, prepared by treatment of jV-methyl-3-methylindole with 2-nitrobenzenesulfenyl chloride, was converted to the rearranged benzothiazine 93 by treatment with triethyl phosphite under nitrogen.137... 

Preparation. The reagent is prepared1 in 67% yield by the Arbusov reaction of triethyl phosphite and ally chloromethyl sulfide.2... 

Desulfurative alkylation and acylation. Titanocene bis(triethyl phosphite) promotes desulfurative alkylation of allylic sulfides (dithioacetals) with f-alkyl halides. ... 

Acyl and aroyl disulfides react by a somewhat different route. Both acetyl disulfide (225) and benzoyl disulfide (125) react exothermically with triethyl phosphite at room temperature to produce 0,0,0-triethyl phosphorothioate and the acyl or aroyl sulfide. This result suggests that the acyl-sulfur linkage in the phosphonium intermediate is more susceptible to cleavage by mercaptide ion than is the alkyl-oxygen bond. 

That a typical free radical initiator, azobisisobutyronitrile, would also catalyze this process was demonstrated by Walling and Rabinowitz (299,300), who proposed direct reaction of thiyl radicals on phosphite to yield an intermediate phosphoranyl radical identical to that produced in the homolytic reaction of disulfides with phosphites. For thiophenol and triethyl phosphite, an ionic reaction to produce phenyl ethyl sulfide and diethyl phosphite is favored even in the presence of di- cr butyl peroxide (298). 

Phenoxazines and phenothiazines 32 and 33 are also made by reductive cyclization of o-nitrodiphenyl ethers or o-nitrodiphenyl sulfides, respectively, with triethyl phosphite. 

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