Triphenylphosphine, reductive cleavage

Cyclization of an allyl A-acyl-1 -phenylglycinate (398) with triphenylphosphine, hexa-chloroethane and triethylamine affords a 2-allyl-3-oxazolin-4-one (400) (81AG(E)395, 77AG(E)394). Reductive cleavage of the oxazolinone with chromium(II) acetate and aqueous hypophosphorous acid furnishes a j3,y-unsaturated ketone (Scheme 88). 

Deprotection of allyl or allyloxycarbonyl derivatives of amino acids.1 This combination of reagents effects rapid reductive cleavage of allyl or allyloxycarbonyl derivatives of amino acids in CH2C12 containing a proton donor (p-N02C6H50H, acetic add, H20). The actual catalyst is probably bis(triphenylphosphine)palladium(0). Benzyl, Boc, and Cbo groups are stable to these conditions. This cleavage does not induce racemization. 

The o-acylaminobenzylphosphonium salts are available from two ways (1) reduction of o-nitrobenzylphosphonium saltZ with zinc in hydrobromic acid-ethanol (yield 95%). The reductive cleavage of the carbon-phosphorus bond can be avoided by using only two equivalents of reagent (2) condensation of o-aminobenzyl alcohols with triphenylphosphine and hydrobromic acid. 

The nitrogen-sulfur bond in 161 (X = S, R = NPhth X = S02, R = OMe) is easily broken under certain conditions. For instance, attempts to obtain a palladium-catalyzed carbonylation reaction with the iodide gave only the ring-opened disulfide 162 and the sulfonic acid 163, presumably by reductive cleavage of the N-S bond by the triphenylphosphine in the reaction mixture <2000T5571>. 

The deoxygenation of epoxides is not of great preparative value since it involves some loss of stereochemical integrity and the alkenes produced are more readily approached in other ways. Reductive cleavage of ozonides, for example, using triphenylphosphine, commonly forms part of the ozonolysis procedure for conversion of alkenes into carbonyl compounds. If a carbonyl compound is treated with an appropriate P(III) reagent then the reverse process may occur—reductive coupling to form a new C=C double bond. This has found a particularly important... 

The reductive cleavage of several aryl disulphides to thiols by their reaction with triphenylphosphine in aqueous dioxan has been reported. Several examples have been reported of the cleavage by phosphines and phosphites of S—SandS—N bonds contained in heterocyclic ring systems. Examples include (73) and (74). ... 

Treatment of alkylsulfenyl methyl thiocarbonates derived from alkyl thiols and Scm-Cl with triphenylphosphine at 0 °C in benzene generates 5 alkyl methyl thiocarbonates in good yield (78% for alkyl = benzyl) (eq 13). Arylsulfenyl methyl thiocarbonates do not parallel this behavior vs. triphenylphosphine but they react cleanly with tributylphosphine (e.g., in dioxane-water) to generate the free arylthiol (see below).The reductive cleavage of alkylsulfenyl methyl thiocarbonates with trialkylphosphines (McsP, EtsP, BU3P) can be achieved with practically quantitative yields in protic solvents (THF-water) in the presence of acids... 

One-electron reversible reduction of triarylphosphine sulfides in DMF/Et4NI leads to an anion radical [198, 203, 204]. The second step of the reduction, occurring at slightly more negative potentials, results in different products of cleavage of P—S or P—C bonds - triphenylphosphine, benzene, and diphenylthiophosphinic acid (Scheme 42). 

---