Enantioselective Reactions of Donor/Acceptor Carbenoids Derived from α-Aryl-α-Diazoketones

Abstract

The reaction of a variety of alpha-aryl-alpha-diazo ketones with activated olefins, catalyzed by the adamantyl glycine-derived dirhodium complex Rh(2)(S-PTAD)(4), generates cyclopropyl ketones with high diastereoselectivity (up to >95:5 dr) and enantioselectivity (up to 98% ee). Intermolecular C-H functionalization of 1,4-cyclohexadiene by means of carbenoid-induced C-H insertion was also possible with this type of carbenoid.

On the Structure of Chiral Dirhodium(II) Carboxylate Catalysts: Stereoselectivity Relevance and Insights

“…Fox model was very well supported by the results obtained earlier for Rh 2 (S-PTAD) 4 by being more enantioselective than Rh 2 (S-PTTL) 4 [37,[91][92][93]95,96]. The results were very relevant as the much bulkier adamantyl groups would more efficiently block the carbene ligands from coordinating to the achiral rhodium face (shrouded by the adamantly groups) compared to the tert-butyl groups of Rh 2 (S-PTTL) 4 leading to the observed more enantioselective outcome.…”

“…Accordingly, they introduced Rh 2 (S-PTAD) 4 catalyst which is derived from L-adamantylglycine ligands (Scheme 6b) [37]. As expected, this catalyst succeeded to afford enantioselectivity levels superior to Rh 2 (S-PTTL) 4 in different asymmetric transformations [37,88,[91][92][93][94][95]. For example, Rh 2 (S-PTAD) 4 -catalyzed cyclopropanation of styrene with α-diazobenzylphosphonate resulted into the generation of the corresponding cyclopropylphosphonate product in high levels of enantioselectivity (99% ee) compared to Rh 2 (S-DOSP) 4 (34% ee), Rh 2 (S-biTISP) 2 (88% ee) and Rh 2 (S-PTTL) 4 (97% ee) (Scheme 6b) [37].…”

“…For example, Rh 2 (S-PTAD) 4 -catalyzed cyclopropanation of styrene with α-diazobenzylphosphonate resulted into the generation of the corresponding cyclopropylphosphonate product in high levels of enantioselectivity (99% ee) compared to Rh 2 (S-DOSP) 4 (34% ee), Rh 2 (S-biTISP) 2 (88% ee) and Rh 2 (S-PTTL) 4 (97% ee) (Scheme 6b) [37]. in different asymmetric transformations [37,88,[91][92][93][94][95]. For example, Rh2(S-PTAD)4-catalyzed cyclopropanation of styrene with α-diazobenzylphosphonate resulted into the generation of the corresponding cyclopropylphosphonate product in high levels of enantioselectivity (99% ee) compared to Rh2(S-DOSP)4 (34% ee), Rh2(S-biTISP)2 (88% ee) and Rh2(S-PTTL)4 (97% ee) (Scheme 6b) [37].…”

Catalytic asymmetric C–H insertion reactions of α-diazocarbonyl compounds

“…67 High enantioselectivity in the intermolecular C-H insertion of α-aryl-α-diazoketones with cyclohexadiene has also been achieved (89% ee). 68 …”

“…175 In such cases, the adamantyl complex Rh 2 (S-PTAD) 4 has been found to be an excellent substitute catalyst for Rh 2 (S-DOSP) 4 (Table 32, entries a-e). 67,68 4 COn-Pr 81 80…”