6.18 Eliminations to Form Alkenes, Allenes, and Alkynes and Related Reactions

Biggs, Robyn Aryn; Ogilvie, William W.

doi:10.1016/b978-0-08-097742-3.00627-3

Cited by 1 publication

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“…The subsequent elimination in Path 1 was examined for both alkoxide intermediates Int3- S , R c and Int3- R , R c and was found to follow an E1cb mechanism via carboanions Int5- S and Int5- R , respectively (Scheme ). The overall barriers of E1cb for the generation of the ( S ) product and ( R ) product are 11.5 and 16.1 kcal/mol, respectively, which are much lower than the epimerization barrier (27.7 kcal/mol) of the chiral axis in Int3- S , R c .…”

Section: Resultsmentioning

confidence: 99%

A Stereodivergent–Convergent Chiral Induction Mode in Atroposelective Access to Biaryls via Rhodium-Catalyzed C–H Bond Activation

Liu

Wang

et al. 2022

ACS Catal.

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Understanding the reaction mechanisms, particularly the chiral induction mode, is critical for the development of new asymmetric catalytic reactions. Rhodium(III)-catalyzed C–H activation en route to atroposelective [4 + 2] annulative coupling with α-diazo β-ketoesters has been realized, affording axially chiral phenanthrenes in good to excellent enantioselectivity. A combination of experimental and computational studies revealed a nontraditional stereodivergent–convergent chiral induction mode. The reaction proceeded with a rhodafluorene intermediate, followed by competitive, constructive, and stereodivergent migratory insertions of the two Rh–C(aryl) bonds into the carbene species to give β-ketoester intermediates. Then, the other Rh–C(aryl) bond migratorily inserts into the ketone carbonyl group. Following this stereodetermining carbonyl insertion, an ester-chelated rhodium(III) alkoxide species bearing two poorly controlled chiral centers and a well-controlled C(sp2)–C(sp3) chiral axis is generated. The final product is delivered via stereoconvergent elimination of a rhodium(III) species with retention of the well-controlled axial chirality and with loss of the central chirality.

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Section: Resultsmentioning

confidence: 99%