Development of Chiral Spiro Phosphoramidites for Rhodium-Catalyzed Enantioselective Reactions

A series of 1,1'-spirobiindane-7,7'-diol (SPINOL) analogues bearing a 2,2'-dimethyl-, cyclopentyl-, or cyclohexyl-fused ring were synthesized, and their distinct structural features were elucidated by X-ray crystallography. On the basis of these scaffolds, chiral monophosphoramidite ligands 6 a-m were synthesized, which demonstrated excellent enantioselectivity in Rh^I -catalyzed asymmetric hydrogenation of a dehydro amino acid methyl ester. Ligands 6 a-m were also successfully applied in the Rh^I -catalyzed enantioselective [4+2] cycloaddition of α,β-unsaturated imines with isocyanates, which afforded the corresponding pyrimidinones in good yields (60-92 %) with high enantioselectivities (75-92 % ee).