Accessing para-Alkylphenols via Iridium-Catalyzed Site-Specific Deoxygenation of Alcohols

Abstract

An iridium-catalyzed and phenol-directed deoxygenation of benzylic alcohols comes as an alternative access to 4alkylphenols, featuring low catalyst loading (S/C up to 20,000, TOF up to 12,400 h −1 ), high functionality compatibility, and excellent site-selectivity. The applications in late-stage modification of steroids and gram-scale total synthesis of a Gastrodia elata extract are highlighted. Mechanistically, the intermediacy of quinone methide controls the site-selectivity, and the formation of iridium hydride serves as the rate-limiting step.

PyBox–La(OTf)3-Catalyzed Enantioselective Diels–Alder Cycloadditions of 2-Alkenoylpyridines with Cyclopentadiene

“…The key factor that underlies this protocol is the choice of a chiral ligand. Our previous research with didentate pyridyl imidazolines [19][20][21][22] led us to consider similar chirally modified nitrogen ligands. Considering the special coordination numbers of rare earth salts, we designed and synthesized several tridentate chiral nitrogen ligands and evaluated their chirality transfer ability in the rare earth-catalyzed Diels-Alder cycloadditions between 2-alk-2-enoylpyridines and cyclopentadiene.…”

Ph3P/ICH2CH2I-promoted reductive deoxygenation of alcohols

“…Transition metal catalysis, which usually involves the activation of alcohols by oxidative addition to transition metals or a heterolytic cleavage of the C–OH bond under acidic conditions to form carbocations, can be applied to primary, secondary and tertiary alcohols (Scheme 1B, path c). 8 This strategy has demonstrated a wide substrate scope and good functional group compatibility, but the use of an expensive transition metal complex is usually necessary. Alcohols can be first activated by a Lewis acid (LA) and would then readily undergo reduction with a hydrogen source (Scheme 1B, path d).…”