Photoinduced Five-Component Radical Relay Aminocarbonylation of Alkenes.

Radical single carbonylation reactions with CO constitute a direct and robust strategy toward various carbonyl compounds from readily available chemicals, and have been extensively studied over the past decades. However, realizing highly selective catalytic systems for controlled radical double carbonylation reactions has remained a substantial challenge, particularly for the more advanced multicomponent variants, despite their great potential value. Herein, we report a visible-light-driven radical relay five-component radical double aminocarbonylation reaction of unactivated alkenes using CO under metal-free conditions. This protocol provides direct access to valuable γ-trifluoromethyl α-ketoamides with good yields and high chemoselectivity. Crucial was the identification of distinct dual roles of amine coupling partners, sequentially acting as electron donors for the formation of photoactive electron donor-acceptor (EDA) complexes with radical precursors and then as a CO acceptor via nitrogen radical cations to form carbamoyl radicals. Cross-coupling of carbamoyl radicals with the acyl radicals that are formed in an alkene-based relay process affords double aminocarbonylation products.

Catalytic Asymmetric Construction of Axially and Centrally Chiral Heterobiaryls by Minisci Reaction.

Axially chiral biaryls and heterobiaryls constitute the most represented subclass of atropisomers with prevalence in natural products, bioactive compounds, privileged chiral ligand/catalysts, and optically pure materials. Despite many ionic protocols for their construction, radical-based variants represent another highly desirable and intriguing strategy but are far less developed. Moreover, efficient synthesis of axially chiral heterobiaryl molecules, especially ones having multiple heteroatoms and other types of chiral elements, through radical routes remains extremely limited. We herein disclose the first catalytic asymmetric, metal-free construction of axially and centrally chiral heterobiaryls by Minisci reaction of 5-arylpyrimidines and α-amino acid-derived redox-active esters. This is enabled by the use of 4CzIPN as an organic photoredox catalyst in conjunction with a chiral phosphoric acid catalyst. The reaction achieved a variety of interesting 5-arylpyrimidines featuring the union of an axially chiral heterobiaryl and a centrally chiral α-branched amine with generally excellent regio-, diastereo-, and enantioselectivity (up to 82% yield; >19:1 dr; >99% ee). This finding also builds up a new platform for the development of desymmetrization methods via radical-involved atroposelective functionalization at heteroarene of prochiral heterobiaryls.

Sesquiterpene lactones from Scorzonera austriaca.

Six new sesquiterpene lactones, scorzoaustriacoside (1), scorzoaustriacin (2), scorzoaustriacin 3-O-beta-d-glucoside (3), 4-epi-dihydroestafiatol (4), 14-isovaleroxyscorzoaustricin (5), and 14-isovaleroxyscorzoaustricin sulfate (6), along with five known guaianolides, were isolated from an acetone extract of the roots of Scorzonera austriaca. The structures of the new compounds were elucidated mainly by interpretation of their 1D and 2D NMR and HRMS data. Several isolates obtained in this investigation were evaluated against a small panel of cancer cell lines.