Phosphoramide catalyst

For a recent summary of the Lewis-base-catalyzed allylation with a main focus on phosphoramide catalysts, see S. E. Denmark, J. Fu, Chem. 

The reaction of simple cyclic vinyl aziridines with organozinc reagents typically provides the 1,4-addition product <2003TL8559>. Several binaphthyl phosphoramidate ligands were examined. In all cases, the /ra r-product 159a was the major product. When no catalyst was used a roughly 1 1 mixture of the trans. cis product was obtained. The use of the chiral phosphoramidate catalyst provided 159a with moderate % ee values (Equation 43). 

Chiral phosphoramides, particularly C2-symmetric examples, are widely used in asymmetric synthesis (see section 3.2). One example is the asymmetric catalysis of Aldol reactions, where the phosphoramide catalyst is used in combination with a Lewis base. A solid state and solution study of the structure of chiral phosphoramide-tin complexes used in such reactions has now been reported. A number of chiral, non-racemic cyclic phosphoramide receptors (387) have been synthesised and their interactions with homochiral amines studied using electrospray ionisation MS. Although (387) bind the amines strongly, no evidence of chiral selectivity was found. Evidence from a combination of its X-ray structure, NMR, and ab initio calculations suggests that the cyclen phosphorus oxide (388) has an N-P transannular interaction in the solid state. A series of isomers of l,3,2-oxazaphosphorino[4,3-a]isoquinolines(389), containing a novel ring-system, have been prepared and their stereochemistry and conformation studied by H, C, and P NMR spectroscopy and X-ray crystallography... 

Very recently, notable advances in this area have been developed by Denmark et al. [100], who succeeded in developing the first catalytic asymmetric sulfenylation of simple alkenes bearing OH groups with iV-(phenylthio) phthalimide and methanesulfonic acids catalyzed by BlNAM-based phosphoramide catalyst 33 (Scheme 14.34) [100]. After intensive preliminary study of the reaction conditions,... 

Studies directed toward the selection and application of an exogenous nucleophile for use with this SiCLj/phosphoramide system first focused on the use of allyltri-butylstannane 20 [35]. The stannane is a competent nucleophile in a wide variety of Lewis acid-promoted carbonyl addition reactions [13, 36-38], and in this system it would provide an effective trap for the ionized chloride through formation of tributyltin chloride. Initial experiments using the optimal phosphoramide catalyst (/ )-10 for the SiCL-mediated opening of meso-epoxides gave good yield and a moderate level of enantioselectivity in the addition of the allyl stannane to... 

Chiral Brpnsted acid catalysis of organic reactions has become a rapidly growing area of research, as it offers operational simplicity together with mild reaction conditions. However, the first Brpnsted acid-catalyzed 1,3-DC of diaryl nitrones 17 to ethyl vinyl ether 18 was demonstrated by Yamamoto and coworkers in 2008 [16]. Only 5 mol% of chiral phosphoramide catalyst 20 was enough for this transformation. Similar to some Lewis acid-catalyzed 1,3-DC reaction, this protocol provided the endo products as the major diastereomers (Scheme 2.7). 

An analogous propargylation can be attained with allenyl tributylstannane however, this reaction is catalyzed by SiCk that is activated by a bis-phosphoramide catalyst. Note that, in this case, the role of the Lewis basic phosphoramide is to increase the Lewis acidity of SiCLj rather than to increase the nucleophiUcity of the stannane [66bj. For a discussion of these effects, see Section 15.4. ... 

Denmark has introduced an innovative approach in catalysis that employs chiral phosphoramide catalysts for the enantioselective addition of allyltriha-losilanes to aldehydes (Equation 16 and Scheme 5.34) [129-133]. 

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