Catalytic asymmetric crotylation of aldehydes: application in total synthesis of (−)‐elisabethadione

A new, highly efficient Lewis base catalyst for a practical enantio- and diastereoselective crotylation of unsaturated aldehydes with E- and Z-crotyltrichlorosilanes has been developed. The method was employed as a key step in a novel asymmetric synthesis of bioactive serrulatane diterpene (À)-elisabethadione. Other strategic reactions for setting up the stereogenic centers included anionic oxy-Cope rearrangement and cationic cyclization. The synthetic route relies on simple, high yielding reactions and avoids use of protecting groups or chiral auxiliaries

Catalytic asymmetric crotylation of aldehydes: application in total synthesis of (−)‐elisabethadione

A new, highly efficient Lewis base catalyst for a practical enantio- and diastereoselective crotylation of unsaturated aldehydes with E- and Z-crotyltrichlorosilanes has been developed. The method was employed as a key step in a novel asymmetric synthesis of bioactive serrulatane diterpene (À)-elisabethadione. Other strategic reactions for setting up the stereogenic centers included anionic oxy-Cope rearrangement and cationic cyclization. The synthetic route relies on simple, high yielding reactions and avoids use of protecting groups or chiral auxiliaries

Asymmetric total synthesis of (-)-erogorgiaene and its C11 epimer and investigation of their antimycobacterial activity

A short, nine-step, highly enantioselective synthesis of (−)-erogorgiaene and its C-11 epimer is reported. The key stereochemistry controlling steps involve catalytic asymmetric crotylation, anionic oxy-Cope rearrangement and cationic cyclisation. (−)-Erogorgiaene exhibited promising antitubercular activity against multidrug-resistant strains of Mycobacterium tuberculosis

Highly stereoselective synthesis of z-homoallylic alcohols by kinetic resolution of racemic secondary allyl boronates

α to Z: Racemic α-chiral allyl boronates, which are readily synthesized from the respective primary allyl halides, undergo a highly efficient kinetic resolution in a face- and Z-selective allylation of aldehydes catalyzed by the chiral Brønsted acid (R)-TRIP (see scheme; Epin=tetraethylethylene glycol). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Cross-aldol reactions of ketones catalyzed by leucinol: a mechanistic investigation

Comprehensive mechanistic studies on the enantioselective aldol reaction between isatin (1 a) and acetone, catalyzed by L-leucinol (3 a), unraveled that isatin, apart from being a substrate, also plays an active catalytic role. Conversion of the intermediate oxazolidine 4 into the reactive syn-enamine 6, catalyzed by isatin, was identified as the rate-determining step by both the calculations (ΔG≠=26.1 kcal mol−1 for the analogous L-alaninol, 3 b) and the kinetic isotope effect (kH/kD=2.7 observed for the reaction using [D6]acetone). The subsequent reaction of the syn-enamine 6 with isatin produces (S)-2 a (calculated ΔG≠=11.6 kcal mol−1). The calculations suggest that the overall stereochemistry is controlled by two key events: 1) the isatin-catalyzed formation of the syn-enamine 6, which is thermodynamically favored over its anti-rotamer 7 by 2.3 kcal mol−1; and 2) the high preference of the syn-enamine 6 to produce (S)-2 a on reaction with isatin (1 a) rather than its enantiomer (ΔΔG≠=2.6 kcal mol−1)

Highly enantio- and diastereoselective generation of two quaternary centers in spirocyclopropanation of oxindole derivatives

Spirocyclopropanes: only one out of eight possible stereoisomers was obtained in the asymmetric cascade cyclopropanation of alkylidene oxindoles with ethyl 2-chloroacetoacetate. Improved catalyst design ensured that spirocyclopropyl oxindoles featuring two quaternary centers were synthesized in high yield and high enantio-and diastereoselectivity