All-Carbon Quaternary Stereocenters α to Azaarenes via Radical-Based Asymmetric Olefin Difunctionalization

Abstract

A radical-based asymmetric olefin difunctionalization strategy for rapidly forging all-carbon quaternary stereocenters α to diverse azaarenes is reported. Under cooperative photoredox and chiral Brønsted acid catalysis, cyclopropylamines with αbranched 2-vinylazaarenes can undergo a sequential two-step radical process, furnishing various valuable chiral azaarene-substituted cyclopentanes. The use of the rigid and confined C 2 -symmetric imidodiphosphoric acid catalysts achieves high enantio-and diastereo-selectivities for these asymmetric [3 + 2] cycloadditions.

Photoredox Catalytic Phosphite‐Mediated Deoxygenation of α‐Diketones Enables Wolff Rearrangement and Staudinger Synthesis of β‐Lactams

“…A cyclic voltammetry study showed that 1,3,2-dioxaphosphole INT1 had a halfwave oxidation potential of + 0.696 V (vs. SCE in CH 3 CN, Scheme 2 c, see Supporting Information for details), well below the reduction potential of excited state DPZ (E t (S*/ SC À ) =+ 1.42 V vs. SCE in CH 3 CN). [14] Fluorescence quenching experiments (Scheme 2 d) finally concluded that INT1 was an active reductive quencher of the excited DPZ (*DPZ).…”

“…[13] We began our investigation with benzil and triethyl phosphite as the model substrate and the deoxygenation reagent, respectively. With the irradiation of a 3 W blue LED (450 nm) and the catalysis of a dicyanopyrazine derived chromophore (DPZ) photosensitizer, [8,14] benzil underwent swift deoxygenation and Wolff rearrangement, affording a ketene intermediate which was trapped by ethanol (Table 1). Under optimized conditions, a,a-diphenylacetate 2 a was obtained in excellent yield (90 %, entry 6).…”

Visible‐Light‐Mediated Ring‐Opening Reactions of Cyclopropanes

“…In 2020, Jiang and co-workers reported the asymmetric reaction of cyclopropylamines 62 with vinyl azaarenes 77 for the construction of an all-carbon quaternary stereocenter at the α-position of azaarenes 78 (Scheme 48). [92] The reaction was performed under a cooperative photoredox and chiral Brønsted acid catalysis. Dicyanopyrazine-derived chromophore (DPZ) was used as the photocatalyst whereas BINOL derived imidodiphosphoric acid C3 was used as the Brønsted acid catalyst.…”

“…Asymmetric reaction of cyclopropylamines with vinyl azaarenes. [92] utility of the obtained products 80 was shown by removing the urea directing group to get aminocyclopentane derivatives.…”

Recent Advances of Dicyanopyrazine (DPZ) in Photoredox Catalysis

“…A rapidly growing number of chemical transformations employs DPZs as photocatalysts [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63]. In 2020, Jiang et al reported a radical-based asymmetric olefin difunctionalization strategy for rapidly forging all-carbon quaternary stereocenters α to diverse azaarenes (Scheme 4) [64]. Under cooperative DPZ as photoredox and chiral Brønsted acid catalysis, cyclopropylamines 9 with α-branched 2-vinylazaarenes 10 can undergo a sequential two-step radical process, furnishing various valuable chiral azaarene-substituted cyclopentanes 11.…”