Asymmetric cyanocarbonation

Scheme 7.18 Asymmetric cyanocarbonation of benzaldehyde using ligand 26.

Ketones have been enantioselectively cyanocarbonated to give tetrasubstituted carbon stereocentres (84), using cinchona alkaloid catalysts and cyano esters, with ees up to 97%.254 A fall-off in ee at high conversions has been explained by a mechanism involving competing asymmetric processes, and significant retro-cyanation. 

The development of the first highly enantioselective cyanocarbonation of prochiral ketones promoted by a chiral base catalyst, such as a cinchona alkaloid derivative, was reported by Tian and Deng in 2006. " Importantly, the reaction complemented known enzyme- and transition metal based methods in substrate scope via its unique ability to promote highly enantioselective cyanocarbonation of sterically hindered simple dialkyl ketones. Mechanistic studies provided experimental evidence to shed significant light on the asymmetric induction step in which the modified cinchona alkaloid acted as a chiral nucleophilic catalyst. Moreover, experimental evidence supported the mechanistic proposal that the enantioselectivity determination step in the cyanocarbonation was a DKR of the putative intermediates G and H via asymmetric transfer of the alkoxycarbonyl group (Scheme 2.105). 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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