Ligand-Induced Selectivity in the Rhodium(II)-Catalyzed Reactions of α-Diazo Carbonyl Compounds

Development of Dirhodium(II)-Catalyzed Generation and Enantioselective 1,3-Dipolar Cycloaddition of Carbonyl Ylides

“…The viability of the substrates 2 to undergo the desired ylide formation/cycloaddition process was established by treatment with rhodium(ii) acetate in CH 2 Cl 2 heated under reflux (60 ± 80 % yields of cycloadducts 3); these racemic cycloadducts were also used for establishing enantiomeric purity determination assays (vide infra). The use of a copper catalyst 6 ([Cu(MeCN) 4 ]PF 6 bisoxazoline ligand), as used by Doyle to affect enantioselective cyclopropanation, [14] and more recently in enantioselective 2,3-sigmatropic rearrangements of oxonium and iodonium ylides, [15] proceeded only sluggishly in CH 2 Cl 2 heated under reflux overnight to deliver optically inactive cycloadduct 3 c (25 % yield, 100 % based on recovered 2); the use of copper-based catalysts was not further pursued. At this stage, representatives of the known classes of chiral rhodium(ii) catalysts, selected for their varying electronic and steric properties and ability to induce enantioselectivity in other diazocarbonyl transformations, [3,5] were screened with the cycloaddition substrates 2, generally both in chlorinated and (where the catalyst was sufficiently soluble) hydrocarbon solvents.…”

“…However, prior to our work, Padwa and co-workers had observed rhodium(ii)-catalyst-dependent changes in regiochemistry during intramolecular cycloaddition following carbonyl ylide formation. [6] Also, there were scattered reports of enantioselective rearrangements, based on transition-metal catalysis, involving other types of ylides from diazo compounds, which could also be interpreted as implying catalyst association with the ylide during the rearrangement step. [7] In this paper we detail our studies on the realisation of enantioselective tandem carbonyl ylide formation/cycloaddition, [8] which have involved the synthesis and examination of a number of new chiral rhodium(ii) catalysts to generate cycloadducts in up to 90 % ee in this emerging asymmetric process.…”

The interaction of rhodium carbenoids with carbonyl compounds as a method for the synthesis of tetrahydrofurans

“…Another study which originated from the authorÕs laboratory provides even more definitive support for the involvement of a metal associated dipole in a diazo catalyzed cycloaddition reaction [35]. A series of competition experiments were carried out using diazoketone 39 (Scheme 12).…”

Tandem Cyclization‐Cycloaddition Reactions of Rhodium Generated Carbenoids from α‐Diazo Carbonyl Compounds.

“…The effect of two different carbonyl groups in the same molecule on ylide formation and subsequent 1,3-dipolar cycloaddition has been probed, 89 the Rh(II)-catalyzed decomposition of the symmetrical dibenzoyl system 183 giving the cycloadduct 185 (Scheme 56). The regiochemical outcome of the reaction is understandable on the basis of electronic and conformational factors.…”