Rh2(ii)-catalyzed enantioselective intramolecular Buchner reaction and aromatic substitution of donor-donor carbenes

The chiral dirhodium(ii) tetracarboxylate-catalyzed enantioselective intramolecular Buchner reaction of donor/donor-carbenes was reported and a series of valuable chiral polycyclic products were synthesized. Both aryloxy enynones and diazo compounds were efficient carbene precursors for this reaction. Excellent yields (up to 99%) and outstanding enantioselectivities (up to >99% ee) were achieved under standard conditions. For furyl substituted chiral cyclohepta[b]benzofurans bearing a substituent at the C4 position on cycloheptatrienes, control reactions showed that the chiral Buchner products could slowly racemize either under dark or natural light conditions. A diradical-involved mechanism rather than a zwitterionic intermediate was proposed to explain the racemization. Furthermore, furyl substituted chiral fluorene derivatives were obtained via asymmetric aromatic substitution when biaryl enynones were employed as carbene precursors.

Automated summary

The chiral dirhodium(ii) tetracarboxylate-catalyzed enantioselective intramolecular Buchner reaction of donor/donor-carbenes was reported, leading to the synthesis of valuable chiral polycyclic products. Both aryloxy enynones and diazo compounds served as efficient carbene precursors. Excellent yields and outstanding enantioselectivities were achieved. The racemization of one product under specific conditions was explained through a proposed diradical-involved mechanism. Furthermore, asymmetric aromatic substitution with biaryl enynones as carbene precursors allowed for the synthesis of furyl substituted chiral fluorene derivatives.