Aldehydes reaction with triphenyl phosphite

An alternative method for the synthesis of proline-related phosphonates is attractive because peptides with a C-terminal Prop(OPh)2 22 can be obtained directly (Scheme 15) J43l The real intermediate reacting with triphenyl phosphite remains unknown but it is very likely that it is a cyclic A-acyliminium ion. Thus, the reaction could be similar to the amidoal-kylation of triphenyl phosphite with carbamates and aldehydes. 

Catalytic one-pot procedure. Since in the described teUuronium ylide olefmation tellurox-ide is formed as a by-product, and the telluroxide is susceptible to reduction by triphenyl phosphite, a catalytic procedure can be employed, providing a practical one-pot synthesis of a, -unsaturated esters and ketones (method E). By this procedure, a catalytic amount of n-dibutyl telluride reacts with the a-bromoester or a-bromoketone, and the formed tel-luronium salt is converted in situ under phase transfer conditions (solid KjCOj/trace HjO) into the ylide, which reacts in turn with the aldehyde, giving the olefin. Since the reaction is performed in the presence of triphenyl phosphite, the formed dibutyl telluroxide is reduced back to the dibutyl telluride, which is then recycled. 

The condensation of an aldehyde, benzyl carbamate, and triphenyl phosphite, first described by Oleksyszyn et al., 25,26 affords a direct route to a-aminoalkylphosphonates 4 that are conveniently protected for subsequent reactions (Scheme 4). Since dealkylation of the quaternary phosphonium intermediate 3 is not possible in this case, formation of the pen-tavalent product 4 presumably involves activation of the solvent and formation of phenyl acetate. This method is useful for the synthesis of aliphatic and aromatic amino acid analogues. However, monomers with more elaborate side chains are often incompatible with the reaction conditions. The free amine can be liberated by treatment with HBr/AcOH or by hydrogenolysis after removal of the phenyl esters. The phosphonate moiety can be manipulated by ready exchange of the phenyl esters in alkaline MeOH and activation as described in Section 10.10.2.1.1. Related condensations with other trivalent phosphite derivatives have been reported. 27-30 ... 

The mechanism of the reaction is not clear, but it is possible that aldehydes react with benzyl carbamate first, to give a (l-hydroxyalkyl)carbamate and then eliminate HzO providing a route to the TV-acyliminium cation that, in the next step, is trapped by triphenyl phosphite. 

The trimethylsilylated ylides (1), easily generated from trimethyl chlorosilane and ylides, react with aldehydes 2 to form vi-nylsilanes 3 (2,3). The vinylphosphonium silanolates 4 are also formed. Compounds 3 are versatile reagents for further reactions (4). The ylide J (with R1 =H) reacts with aldehydes 2 to give the dienes j). The oxidation of with the adduct 6, from triphenyl-phosphite and ozone, gives access to a generaT synthesis of acyl-silanes (trimethylsilylketones) (2). The silylated ylides react to form phosphonium salts 7 with halogen compounds. The salts 7.can be desilylated by fluorine ions. The disubstituted ylides JO Tormed can be converted in statu nascendi with aldehydes V[ into the tris-substituted olefin J2 (2,3). In the case of R3-I, vinyl... 

Tellurium-Wittig reactions.1 The reaction of aldehydes with a-bromo esters or ketones, triphenyl phosphite, and a weak base in the presence of a catalytic amount of Bu2Te results in ct, l-unsaturated esters and ketones. The function of the triphenyl phosphite is the regeneration of Bu2Te from the dibutyl telluroxide formed in the... 

Several reports of the synthesis and chemistry of benzimidazoles have been published. The most common methods involved the condensation of 1,2-phenylenediamine with a carbonyl group. 2-Substituted benzimidazoles were prepared from 1,2-phenylenediamine and esters under microwave conditions <06SC2597>. A highly selective synthesis of 2-aryl-l-arylmethyl-l/7-1,3-benzimidazoles from the reaction of 1,2-phenylenediamines and aromatic aldehydes in the presence of silica sulfuric acid in ethanol or water has been reported <06TL2557>. Microwave-assisted one-step high-throughput synthesis of benzimidazoles from phenylenediamine and carboxylic acids in the presence of triphenyl phosphite has been disclosed <06TL2883>. A... 

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