Reduction tributylphosphine

U. T. Ruf gg u. J. Rudinger, Reductive Cleavage of cystine disulfides with tributylphosphins, Methods Enzymol. 47, 111 (1977). 

Reductions by Co(I) chelates such as vitamin Bi2s and tributylphosphine-... 

Vanadium chloride, 2 chromium chloride,33 and the combined use of tributylphosphine and diphenyldisulfide34 are also effective in promoting the reductive Nef reaction. 

Recently, Ohmori and coworkers have used an anodic oxidation reaction to promote the reduction of an acid [34]. In this experiment, the anodic oxidation of triphenyl- or tributylphosphine in the presence of a carboxylic acid led to the formation of an acyl phosphonium ion. The acyl phosphonium ion was then reduced at the cathode to form an ylide which then trapped a second carbonyl... 

The formation of N,iV -dialkyl-4,4 -bipyridine cation-radical proceeds through the reduction of the corresponding dication (alkylviologen) by tributylphosphine. Yasui et al. (2001) measured the reaction kinetics in the acetonitrile-methanol mixture. The rate of cation-radical formation decreases in all of the cases when the alkyl groups are deuterated. 

A recent adaptation of this type of approach involves the spontaneous intramolecular cyclization of imino ketones, formed by the reduction of nitro ketones through the action of tributylphosphine/diphenyl sulfide (Scheme 6.14). When the corresponding esters (R = OR) are used, pyrrolin-2-ones are formed (Scheme 6.15). 

Cys(StBu) with phosphines only a slight excess of tributylphosphine is required for this purpose. Under these conditions reduction of the diselenide does not occur at all, and subsequent air oxidation of the two cysteine residues at high dilution leads in a highly selective manner to the diselenide- and disulfide-bridged peptides. The selectivity of the disulfide bridging is assured by the complete absence of thiol/diselenide exchange reactions even at alkaline pH values due to the very low reactivity of the diselenide toward mono-thiols as a result of their highly differentiated redox potentials. ... 

The p-sulfanyl amides 28 are synthesized from N-protected amino acids 24 via amino alcohols 25, which are converted into (5-acetylsulfanyl amides 26 by a Mitsunobu reaction. The (5-amine disulfide 27 is subsequently coupled with a variety of carboxylic acids, followed by reduction with tributylphosphine in aqueous THF in the presence of pyridine to produce the free thiol 28 (Scheme 5).1211 Detailed experimental procedures for these compounds have not been reported. 

Diethyl (trimethylsilyl) phosphine has been prepared by the reaction of lithium diethylphosphide with chlorotrimethyl-silane in ether solution.4 The lithium diethylphosphide may be prepared by the reaction of an ether solution of phenyllithium with diethylphosphine.6 However, the dialkylphosphines are most conveniently prepared by the reduction of the corresponding tetraalkyldiphosphine disulfides with lithium tetrahydro-aluminate in ether.6 7 An alternative method for the preparation of dimethyl(trimethylsilyl)phosphine which eliminates the handling of the volatile dimethylphosphine involves the preparation of lithium dimethylphosphide from tetramethyldiphosphine. The latter is prepared by the reduction of tetramethyldiphosphine disulfide8 with tributylphosphine.9 The reaction of chlorotrimethylsilane with lithium dimethylphosphide is most conveniently carried out in a vacuum system without solvent at -78°. 

Of the 78 survey responses only 22 reported that they routinely alkylate samples before sequencing. However, 49 facilities alkylated ABRF-94SEQ, of which 37 used solution and 12 attempted in situ alkylation. The remaining 29 facilities sequenced without alkylation. Table IV describes several methods of reduction and alkylation that were all provided with ABRF-94SEQ. An additional method using 3-bromopropyl-amine was employed by one respondent. Reduction in solution was performed with dithiothreitol (DTT) (68%), 2-mercaptoethanol (29%), and tributylphosphine (TBP) (3%). In situ reduction was carried out using DTT (50%) and TBP (50%). 

An alternative interesting approach, which is based on the Mukaiyama reduction/oxidation procedure for peptide bond formationt uses tributylphosphine in the presence of diphenyl diselenide and the N-protected annino acid for in situ condensation with the a-azido compound. The phenyl carboselenolate is formed as an activated carboxylic add and the resulting benzeneselenol reduces the azide to the amine for reaction with the active ester. 

Oppolzer has developed a method of asymmetric synthesis based on the use of the chiral auxiliaries 39A and 39B derived respectively from (+ )-camphor [(+ )-40] and (- )-camphor [(- )-40]. Crotonylation of 39A gave the ester that was attacked by 4-methyl-3-pentenyllithium in the presence of copper iodide tributylphosphine and boron trifluoride from only one side of the molecule, the product 41 having the (S)-configuration (enantioselectivity 98.5%). The ester 42—similarly obtainable from 39B—was methylated under similar conditions, also yielding 41 with 92% enantioselectivity. (S)-Citronellic acid [(S)-36] or (S)-citronellol [(S)-33] were then obtained from 41 by the action of sodium hydroxide or lithium aluminum hydride (Scheme 6). Reduction of potassium... 

Initial progress was swift and the two subunits required for the CIO-C16 dithiane fragment, sulfone 12 and aldehyde 10, were easily prepared. Ester 13 was first converted to the mono-protected diol 18 by silylation followed by ester reduction (Scheme 4). The phenyl sulfone auxiliary was next installed in two steps by a Mitsunobu-like thioether formation with diphenyl disulfide and tributylphosphine followed by oxidation with Oxone . The resulting sulfone 19 was desilylated and the liberated hydroxyl group converted to an aldehyde with Swem s procedure. Subunit 12 was completed by formation of the dithiane from aldehyde 20 under standard conditions. 

Phospholes and other related heterocycles are an important class of main group compounds. The chemistry of phospholes and their preparation has been reviewed extensively by Mathey.3 We provide details here for a simple, one-pot procedure for the preparation of 1-phenyl-2,3,4,5-tetramethylphosphole applying zirconocene chemistry.4 The procedure involves reduction of (n-CsHsteZrCIa with butyllithium in the presence of 2-butyne which (as reported initially by Negishi, et al.s) forms a zirconium metallacycle. Addition of dichlorophenylphosphine to this reaction mixture produces the phosphole. One other procedure for the preparation of 1-phenyl-2,3,4,5-tetramethylphosphole has been reported by Nief, et al.2 That procedure involved aluminum chloride - coupling of 2-butyne, followed by reaction with dichlorophenylphosphine to form a chlorophospholium tetrachloroaluminate which was then reduced with tributylphosphine to produce the phosphole in 68% yield. 

Stereoselective reduction of 6-bromopenicillins 88 by tributylphosphine in methanol afforded 89 through formation of an intermediate phosphonium p-Iactam enolate species and subsequent diastereoselective protonation . 

From the numerous additional methods proposed for the protection of the thiol function the o-nitropyridinesulfenyl (Npys) group is mentioned here on account of the interesting reductive cleavage of the intermediate disulfide with tributylphosphine ... 

---