Carbonyl ylide formation-enantioselective

Scheme 7.52 Domino carbonyl ylide formation-enantioselective reduction reaction catalysed by chiral phosphoric acid catalysis and rhodium catalysis followed by benzoylation.

Hodgson and co-workers have studied the intramolecular cascade carbonyl ylide formation-cycloaddition with chiral Rh(ii) catalysts.After screening a series of chiral Rh(ii) catalysts, high enantioselectivity was achieved in the reaction of 98 by using the Rh(ii) catalyst with binaphthyl phosphate-derived chiral ligands dirhodium(ii) tetrakis[(i )-6,6 -didodecylbinaphtholphosphate] [Rh2(i -DDBNP)4] (Equation (13)). 

Enandoselective tandem carbonyl ylide formation-cycloaddition of a-diazo- -keto esters is achieved in hexane with [Rh2(5-DOSP)4] (1 mol %) at room temperature to give the corresponding cycloadducts with moderate enantioselectivity [73] (Eq. 8A.49). 

Another successful catalytic enantioselective 1,3-dipolar cycloaddition of Qf-diazocarbonyl compounds using phthaloyl-derived chiral rhodium(II) catalysts has been demonstrated [ill]. Six-membered ring carbonyl ylide formation from the a-diazo ketone 80 and subsequent 1,3-cycloaddition with DMAD under the influence of 1 mol % of dirhodium(II) tetrakis[M-benzene-fused-phthaloyl-(S)-phenylvaline], Rh2(S-BPTV)4 101 [112], has been explored to obtain the cycloadduct 102 in up to 92% ee (Scheme 31). 

Hashimoto and coworkers accomplished the immobilization of chiral dirhodium (II) catalyst on a polystyrene-based copolymer. The polymer catalyst (55), which was packed in a gravity fed column, was successfully applied in a domino carbonyl ylide formation - dipolar cydoaddition under continuous-flow conditions (Scheme 7.39). The desired bicyclic adduct was obtained in high yield and high levels of asymmetric induction (up to 99% ee). The flow reactor was demonstrated by the retention of activity and enantioselectivity even after 60 h with a low metal leaching level (2.1 ppm) [146]. 

They also reported high levels of enantioselection for the inter-molecular cycloadditions of ester-derived carbonyl ylides with DMAD (up to 93% ee, Rh2(S-PTTL)4) (Scheme 7.22) [58] and a-diazo ketone-derived carbonyl ylides with aromatic aldehydes (up to 92% ee, Rh2(S-BTPV)4) (Scheme 7.21) [59]. Dirhodium (II) tetrakis[A -tetrachIorophthaIoyI-(S)-ferf-Ieucinate], Rh2( 5-TCPTTL)4, was found to be an exceptionally effective catalyst for tandem carbonyl ylide formation/cycloaddition reactions of... 

Intramolecular ylide formation with the lactone carbonyl oxygen (53) in 145 provided a carbonyl ylide 146 that was trapped with Al-phenyl maleimide to give cycloadduct 147. Likewise (54), carbonyl yhde 149, derived from ester 148, suffers intramolecular cycloaddition with the tethered alkene to deliver acetal 150 in 87% yield. An enantioselective version of this process has also been described (Scheme 4.33). 

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... 

Chapter 4 concerns the cycloaddition of carbonyl ylides generated from diazo carbonyl compounds and rhodium or copper catalysts. In this framework chemoselective and enantioselective transformations leading to the formation of various heterocycles such as tetrahydrofurans, oxazolidines, mesoionic and bicyclic compoxmds, alkaloids, and other natural products are described. 

---