Design and Synthesis of C₄-Symmetric Axially Chiral β-Aryl Porphyrins and Application for Supporting Ir(III)-Catalyzed Enantioselective C-H Alkylation.

Abstract

A hitherto unknown class of C4-symmetric Caryl-Cβ (C3, C8, C13, C18) axially chiral porphyrins has been synthesized and the application of their iridium (Ir) complexes in catalytic asymmetric C(sp3)-H functionalization is documented. Cyclotetramerization of enantioenriched axially chiral 2-hydroxymethyl-3-naphthyl pyrroles under mild acidic conditions affords, after oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), the C4-symmetric α,α,α,α-atropenantiomer as an only isolable diastereomer. Both regioisomeric Ir(Por*)(CO)(Cl) complexes catalyze the carbene C-H insertion reaction affording the same enantiomer, albeit with slight difference in enantioselectivity. With the optimum Ir-complex 3e, the 2-substituted arylacetic acid derivatives were generated from diazo compounds and cyclohexadiene in excellent yields and enantioselectivities.