Teerawut Bootwicha

N-Trifluoromethylthiophthalimide: A Stable Electrophilic SCF3-Reagent and its Application in the Catalytic Asymmetric Trifluoromethylsulfenylation†

Cinchona alkaloid catalysts in combination with air- and moisture-stable N-trifluoromethylthiophthalimide as electrophilic SCF3 source enabled the catalytic enantioselective trifluoromethylsulfenylation. Thus, a series of α-SCF3 esters that bear a quaternary carbon stereogenic center were obtained with excellent yield and enantioselectivity. Moreover, the products can be readily converted into valuable α-SCF3 β-hydroxyesters.

Toward Ideality: The Synthesis of (+)-Kalkitoxin and (+)-Hydroxyphthioceranic Acid by Assembly-Line Synthesis

The iterative homologation of boronic esters using chiral lithiated benzoate esters and chloromethyllithium has been applied to the highly efficient syntheses of two natural products, (+)-kalkitoxin and (+)-hydroxyphthioceranic acid. The chiral lithiated benzoate esters (>99% ee) were generated from the corresponding stannanes, which themselves were prepared by Hoppe-Beak deprotonation of ethyl 2,4,6-triisopropyl-benzoate with s-BuLi in the presence of (+)- or (-)-sparteine and trapping with Me3SnCl followed by recrystallization. In addition, it was found that purification between several homologations could be avoided, substantially increasing both chemical and manpower efficiency. In the case of (+)-kalkitoxin, six iterative homologations were conducted on commercially available p-MeOC6H4CH2Bpin to build up the core of the molecule before the C-B bond was converted into the desired C-N bond, without purification of intermediates. In the case of (+)-hydroxyphthioceranic acid, 16 iterative homologations were conducted on p-MeOC6H4Bpin with only four intermediate purifications before oxidation of the C-B bond to the desired alcohol. The stereocontrolled and efficient syntheses of these complex molecules highlight the power of iterative chemical synthesis using boronic esters.

Continuous-flow catalytic asymmetric hydrogenations: Reaction optimization using FTIR inline analysis

Summary The asymmetric organocatalytic hydrogenation of benzoxazines, quinolines, quinoxalines and 3H-indoles in continuous-flow microreactors has been developed. Reaction monitoring was achieved by using an inline ReactIR flow cell, which allows fast and convenient optimization of reaction parameters. The reductions proceeded well, and the desired products were isolated in high yields and with excellent enantioselectivities.

Continuous-flow hydration-condensation reaction: Synthesis of α,β-unsaturated ketones from alkynes and aldehydes by using a heterogeneous solid acid catalyst

Summary A simple, practical and efficient continuous-flow hydration–condensation protocol was developed for the synthesis of α,β-unsaturated ketones starting from alkynes and aldehydes by employing a heterogeneous catalyst in a flow microwave. The procedure presents a straightforward and convenient access to valuable differently substituted chalcones and can be applied on multigram scale.