Asymmetric hydrogentation of unfunctionalised olefins/enamines/imines
The reaction survey found that the predominant strategy for the introduction of chirality was through classical chemical resolutions as opposed to introductions through biotransformation or transition metal or organometallic catalytic means.
Asymmetric hydrogenation provides an elegant methodology for the introduction of chirality, meeting many of the goals of green chemistry and is finding increasing application in API synthesis.47
The efficiency of this approach is elegantly exemplified by the Merck second generation synthesis of sitagliptin 5 (Scheme ), where an unprecedented final stage asymmetric hydrogenation of the unprotected enamide 6 resulted in an increase in overall yield of almost 50% and produced 100 kg less waste per kg sitagliptin48 when compared with the first generation approach.49
|Scheme The synthesis of sitagliptin.|
There are challenging areas remaining within the field, for example, the hydrogenation of enamides and related substrates in the synthesis of amino…
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