Organic Reactions, Volume 93 by unknow

Author:unknow
Language: eng
Format: epub
Publisher: John Wiley & Sons, Incorporated
Published: 2017-07-24T00:00:00+00:00

Scheme 154

Copper Catalysis

Alkylidene cyanoacetates are effective substrates for the 1,4-addition of arylboronic acid neopentylglycol esters catalyzed by a chiral copper/N-heterocyclic carbene complex (Scheme 155).230 The use of potassium tert-butoxide (2.0 equivalents) plays a key role in facilitating catalyst turnover.

Scheme 155

The overwhelming majority of organoboron reagents employed for catalytic, enantioselective 1,4-additions fall into one of the following classes: (hetero)aryl-, alkenyl-, or allylboron reagents. However, copper catalysis has shown success in the catalytic, enantioselective 1,4-addition of alkylboron reagents. Alkyl-9-BBN reagents generated by the hydroboration of terminal alkenes with (9-BBN-H)2 are effective in the conjugate addition to imidazol-2-yl α,β-unsaturated ketones when a copper/N-heterocyclic carbene complex is employed as the catalyst (Scheme 156).231

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