Aldimines hydrophosphonylation

Akiyama et al. disclosed an asymmetric hydrophosphonylation in 2005 (Scheme 32) [55], Addition of diisopropyl phosphite (85a) to A-arylated aldimines 86 in the presence of BINOL phosphate (R)-M (10 mol%, R = 3,5-(CF3)j-C Hj) afforded a-amino phosphonates 87 in good yields (72-97%). The enantioselectivities were satisfactory (81-90% ee) in the case of imines derived from a,(3-unsaturated aldehydes and moderate (52-77% ee) for aromatic substrates. 

Scheme 6.48 Product range of the asymmetric hydrophosphonylation of N-benzylated aldimines promoted by thiourea derivative 47.

Wenzel and Jacobsen reported the thiourea 15b-catalyzed Mannich-type reaction of a ketene silyl acetal with an N-Boc-aldimine, furnishing (3-amino esters with excellent enantioselectivities (Equation 10.30) [59]. Subsequently, Jacobsen and co-workers reported the hydrophosphonylation of dialkyl phosphites with aldimines to yield a-amino phosphonates [60]. 

Some of the metal-based catalysts used in the asymmetric hydrophosphonylation of aldehydes (see Section 6.4) can also be applied to the phosphonylation of imines. For instance, Shibasaki s heterobimetallic BINOL complexes work well for the catalytic asymmetric hydrophosphonylation of imines. In this case lanthanum-potassium-BINOL complexes (6.138) have been found to provide the highest enantioselectivities for the hydrophosphonylation of acyclic imines (6.139). The hydrophosphonylation of cyclic imines using heterobimetallic lanthanoid complexes has been reported. Ytterbium and samarium complexes in combination with cyclic phosphites have shown the best results in the cases investigated so far. For example, 3-thiazoline (6.140) is converted into the phosphonate (6.141) with 99% ee using ytterbium complex (6.142) and dimethyl phosphite (6.108). The aluminium(salalen) complex (6.110) developed by Katsuki and coworkers also functions as an effective catalyst for the hydrophosphonylation of both aromatic and aliphatic aldimines providing the resulting a-aminophosphonate with 81-91% ee. ... 

A number of Bronsted acidic organocatalysts have been applied to the asymmetric hydrophosphonylation of aldimines. Thiourea catalysts related to (6.130) catalyse the asymmetric hydrophosphonylation of a range of aliphatic and aromatic aldimines with high ee and BINOL-derived phosphoric acid derivatives similar in structure to (6.131) are effective catalysts in the asymmetric phosphonylation of cinnamaldehyde-derived aldimines. Asymmetric hydrophosphonylation of aromatic aldimines can also be achieved with high ee using cheap, commercially... 

The hydrophosphonylation reaction of aldimines (173) with phosphites (174) has furnished a-amino phosphonates (175) with high enantioselectivities by means of the chiral phosphoric acid (125) derived from R) BINOL (Scheme 47). ... 

The asymmetric hydrophosphonylation reaction of aldimines (207) with dialkyl phosphites (206) has been reported using catalytical amounts of the phosphoric acid (125), derived from (7 )-BINOL to afford (l )-amino phos-phonates (208) in good to high enantioselectivities (up to 90% cc) (Scheme 58). ... 

Scheme 2.50 Enantioselective hydrophosphonylation to aldimines with the use of chiral heterobimetallic lanthanum(iii) potassium(i) tris(binaphtholate).

For pioneering work on the highly enantioselective one-pot reaction of in situ preformed imines using a chiral salalen-ahiminiim catalyst, see B. Saito, H. Egami, T. Katsuki, J. Am. Chem. Soc. 2007, 129, 1978-1986. Synthesis of an optically active Al(salalen) complex and its application to catalytic hydrophosphonylation of aldehydes and aldimines. 

This catalyst is also effective for hydrophosphonylation of aldimines (Scheme 6.57). In this case, N-substituent of aldimines played an important role and high enantioselectivity was found with N-4-methoxy-3-methylphenyl aldimines. 

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