Amine-catalyzed cyclopropane activation

SCHEME 6.23 Amine-catalyzed cyclopropane activation developed by Gilmour et al. 

Photochemical Fe(CO)5-induced rearrangement of silylated allyl amine 9 gave N-silylated enamine 1015, which on subsequent Cu-catalyzed cyclopropanation by methyl diazoacetate afforded cyclopropane derivative 11. The use of an optically active catalyst gave an asymmetric induction of 56% ee for the cis isomer and 20% ee for the trans isomer. Further acid-induced ring cleavage afforded the -formyl ester 12, whereas reduction and desilylation produced aminocyclopropane carboxylic acid 13 (equation 2). 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Having established the capacity of chiral amines to catalyze asymmetric [4-1-2] and [3-1-2] reactions of unsaturated aldehydes, researchers sought to extend this olefin-activation platform to [2-t-l] reactions to produce three-membered rings. Amazing organocatalytic [2-t-l] reactions, including cyclopropanation, epoxidation, and aziridination, were developed. 

Other ylides have also been used for cyclopropanation. Ley and coworkers reported effective cyclopropanation using chloroketones and an acrylate ester in the presence of DABCO (Scheme 1.28) [47]. In the reaction, N-ylide 43 or 44 was assumed to be generated as an active reaction intermediate. A chiral amine derived from quini-dine 45 catalyzed asymmetric cyclopropanation to give 46 in 94% ee. 

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