Hydrocyanation of imines

Fig. 11 Kunz s hypothesized pre-transition state for the asymmetric hydrocyanation of imines promoted by a novel paracyclophane imine catalyst...

Several organocatalysts have been recycled efficiently (selected examples are shown in Scheme 14.2). For example, the Jacobsen group has reported results from an impressive study of the recycling of the immobilized urea derivative 6, a highly efficient organocatalyst for asymmetric hydrocyanation of imines (Scheme 14.2) [11]. It was discovered that the catalyst can be recycled and re-used very efficiently - over ten reaction cycles the product was obtained with similar yield and enantioselectivity (96-98% yield, 92-93% ee). 

The asymmetric catalytic Strecker reaction is an elegant means of synthesis of optically active a-amino acids. The Jacobsen group developed optimized organocata-lysts [21, 44-48], optically active urea or thiourea derivatives, which were found to be the most efficient type of catalyst yet for asymmetric hydrocyanation of imines (see also Section 5.1 on the hydrocyanation of imines). Because of its high efficiency, Jacobsen hydrocyanation technology has already been used commercially at Rodia ChiRex [49]. The concept of the reaction is shown in Scheme 14.7. In the presence of a catalytic amount (2 mol%) of the readily available organocatalyst... 

Hydrocyanation of imines [5.1] Mannich reaction [5.2] Hydrophosphonylation of imines [5.5]... 

The organocatalytic hydrocyanation of imines provides direct access to a diverse range of aromatic amino nitriles and the corresponding amino acids and diamines in highest enantioselectivities. The use of... 

The catalyzed hydrocyanation of imines (Strecker reaction) has the option of employing a stable (salen)aluminum chloride or a Zr complex of 6,6 -dibromo-BINOL, with BujSnCN. It is important to derive the imines firom o-aminophenol for the present purpose. 

Since the pioneering work by Ojima et al. [653] the Strecker-type reaction of imines bearing a chiral auxihary with TMSCN has frequently been used for asymmetric synthesis of a-aminonitriles [654]. In recent years catalytic asymmetric hydrocyanation of imines with TMSCN has been intensively studied to establish a more efficient route to optically active a-aminonitriles [655]. 

Jacobsen et al. have reported that peptide Schiff bases and an Al-salen complex are valuable for asymmetric hydrocyanation of imines with TBSCN [660] and TMSCN [661], respectively. It is, however, most likely that HCN arising from these cyanosilanes and adventitious water is the reactive nucleophile. Hoveyda et al. also have used TMSCN as a source of HCN in the hydrocyanation of imines catalyzed by a Ti-peptide Schiff base complex [662],... 

The use of supported catalysts in the process of chiral catalyst discovery and optimization has already been described for the highly successful Jacobsen s amino acid-derived thioureas employed to promote the hydrocyanation of imines [12]. 

An optimised chiral binol phosphate catalyst (87) for the hydrocyanation of imines provides a convenient strategy for the enantioselective synthesis of a-amino acids and diamines (Scheme 22). The same catalyst (87) has been used for cascade... 

Table 30.11 Hydrocyanation of imines catalyzed by Bransted acid 88. ...

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