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Asymmetric synthesis of γ-nitrophosphonates in the absence of any other chiral catalysts

Last few decades have seen development of chiral catalysis to an extent where it can be thought of biomimicking. However, source of pure enantiomer still beholds in the technique of classic resolution, biochemical and biological methods. This is due to the fact that most of the asymmetric reactions are not absolute in the sense of selectivity. The present invention envisages that the autocatalytic amplification can be critical leading to the utilization of general reactions where enantiomeric excess is anything but absolute. The exclusion of external ligand for catalysis save costs to a great extent and also removes the necessity to separate the product from catalyst which could further prove economical in commercial applications.

The main disadvantage with the prior art is that the projected speculations for these reactions in the absence of catalyst require three steps to attain such enantioselectivities. The existing process for preparation of aminophosphonates requires addition of other chiral catalysts such as cinchonine [Tetrahedron:Asymmetry,2007,doi:10.1016/j.tetasy.2007.11.001]. Such types of processes are cumbersome and costly.

Thus, there is a need for development in terms of a process for preparation of nitrophosphonates, more particularly, γ-nitrophosphonates which would be first and cost effective.

The present inventors have found a process which by adopting selectively asymmetric autocatalysis, mirror symmetry breaking and absolute asymmetric synthesis in Michael addition produces an amplification of greater than 99% enantiomeric excess (ee) in one step which is about three times superior to that of Soai reaction in literature. The products synthesized and their derivatives are possible drug candidates and their asymmetric synthesis was highly desirable.

Indian patent application no. 2359/MUM/2007 Patent grant no.
Inventors: Irishi N N Namboothiri and Vishal Rai