Additions to Imine Derivatives Bearing N-Bound Auxiliaries

3 Additions to Imine Derivatives Bearing N-Bound Auxiliaries 

The most readily available chiral amines used for such purposes are a-phenethylamine and amines derived from naturally occurring amino acids. The convenience and ease with which the C-N bond can be reduc-tively cleaved in phenethylamine and phenylglycine derivatives prompted numerous early investigations [60]. As an example, Barflcnecht reported that the reduction of the a-phenethylamine-derived ketimine 51 with RaNi produced 52 in 96% ee after hydrogenolysis (Equation 6) [61]. 

In independent studies, Denmark noted that the yields in additions of or-ganometallic species to enolizable SAMP-derived hydrazones such as 78 were generally improved by employing the less basic organocerium reagents (Equation 7) [71]. These findings further expand the scope for the use of SAMP and RAMP chiral auxiliaries in asymmetric C=N additions. 

Chiral N-sulfmyl imines (80) have emerged as an extremely powerful class of building blocks for asymmetric synthesis [24-27, 72). They are conveniently synthesized in high optical purity and there are numerous available procedures to cleave the N-S bond in order to remove the chiral auxiliary. The N-sulfonyl group is strongly electron-withdrawing and thus activates C=N towards nucleophilic attack. 

There have been recent remarkable advances in the field spearheaded by Ellman, who has described the use of optically active N-tert-butylsulfinyl imines 82. As a consequence of Ellman s intense activity in this area, this has evolved into a highly convenient and exceedingly versatile auxiliary for the asymmetric synthesis of a wide range of amines [27]. A key feature in the development of the tert-butyl sulfinyl amide auxiliary is its straightforward 

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