Proazaphosphatrane

The use of stronger bases than, for example, DBU, such as proazaphosphatrane 13 or... 

Proazaphosphatrane, P(RNCH2CH2)3N, is an efficient catalyst for the Henry reaction, and various ketones give nitro-aldols by the reaction with nitromethane and other nitroalkanes (Eq. 3.20).21... 

Verkade JG, Urgaonkar S (2006) Proazaphosphatrane. Encyclopedia for reagents in organic synthesis, doi 10.1002/047084289X.rn00702... 

Recently, Verkade and coworkers have reported the successful synthesis of /3-hydroxy-nitriles from carbonyl compounds in a reaction promoted by strong nonionic bases, such as proazaphosphatrane types. The reaction occurs in the presence of magnesium sulfate. 

The effect of substituents on C(2) of vinyl bromide and on the amine of the palladium catalyst in the. S n reaction with secondary amines was examined. The catalyst formed from the reaction of Pd2(dba)3 with proazaphosphatrane (12) gave the best yields (>91%) of enamine.16 The. S n product formed with primary amines rearranged to give the imine as the product in yields of >86%. 

Head-to-tail dimerisation of methyl acrylate to the dimethyl ester of 2-methylenepentane-dioic acid (126) occurred in 82-85% yield in the presence of catalytic amounts of P(RNCH2CH2)3N with R = PP, Bu or Bz but the less sterically hindered proazaphosphatrane with R = Me, gave oligomer or pol-ymer. The proazaphosphatrane, P(RNCH2CH2)3N with R = Bu also acts as an effective ligand for the palladium-catalyzed direct arylation of ethyl cyano-acetate (127) with aryl bromides (e.g. 128) to form (129) in high yield. ... 

Proazaphosphatrane ligands in combination with Pd2(dba)3 also generate highly active catalysts for Buchwald-Hartwig amination of aryl chlorides, e.g. (132) from (130) and (131). The PAP ligand with R = Bu was particularly effective and the catalyst performed extremely well with sterically hindered substrates. ... 

When aliphatic nitro compounds are used instead of aldehydes or ketones, no reduction occurs, and the reaction has been referred to as a Tollens reaction (see 16-43). However, the classical condensation of an aliphatic nitro compound with an aldehyde or ketone is usually called the Henry reaction or the Kamlet reaction, and is essentially a nitro aldol reaction. A variety of conditions have been reported, including the use of a silica catalyst, Mg—A1 hydrotalcite, a tetraalkylam-monium hydroxide,proazaphosphatranes, " or an ionic liquid.A solvent free Henry reaction was reported in which a nitroalkane and an aldehyde were reacted on KOH powder. Potassium phosphate has been used with nitromethane and aryl aldehydes. The Henry reaction has been done using ZnEt2 and 20%... 

The commercially available proazaphosphatrane (98) has now been shown to be an efficient catalyst for the silylation of tertiary alcohols and hindered phenols by TBDMS. Evidence is presented to suggest that 99, with a transannular N-P bonding component, is the effective intermediate in the catalytic cycle. 

In the hypervalent area of phosphorus chemistry a configurationally stable tris(tetrachlorobenzenediolato) phosphate ion has been synthesised. The growing importance of hydridophosphoranes in coordination chemistry has led to the apprearance of a useful review. The superbase properties of the commercially available proazaphosphatrane has been extended to the catalysis of the silylation of sterically hindered alcohols and phenols. 

Recent applications of proazaphosphatranes in organic synthesis 04ACA3. 

Proazaphosphatrane ligands, such as 420, partnered with palladium species generated highly active catalysts for Buchwald-Hartwig reactions. An example of such transformations was illustrated when 26 was able to react with 413 to afford 414 [149]. 

Three new proazaphosphatrane bases (108ab) and (109) have been prepared and a pKa value of 34.49 reported for (109). A comparison of the catalytic properties of three bases (108c-e) was also made in the synthesis of p-hydroxynit-riles, p-nitroalkanols, a,p-unsaturated esters and for the Michael addition of alkyl alcohol to a,p-unsaturated ketones. ... 

Other Phosphorus Containing Superbases Verkade s Proazaphosphatranes 37... 

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