Phosphine-mediated partial reduction of alkynes to form both (E)- and (Z)-alkenes

Abstract

A mild, phosphine-mediated partial reduction of alkynyl carbonyls to the corresponding alkenes was developed. Tuning of the reaction conditions led to either the (E)- or (Z)-diastereomer with high selectivity. A range of alkynyl esters, amides, and ketones were reduced to form alkenes in good to high yields and with excellent functional group tolerance.

Phosphorus-Recycling Wittig Reaction: Design and Facile Synthesis of a Fluorous Phosphine and Its Reusable Process in the Wittig Reaction

“…[ Z -Isomer (CAS no. 51507-21-2)]: 1 H NMR (400 MHz, CDCl 3 ) δ 8.20–8.26 (overlapped with E -isomer, m, 2H), 7.67–7.73 (overlapped with E -isomer, m, 2H), 7.02 (d, J = 12.7 Hz, 1H), 6.13 (d, J = 12.7 Hz, 1H), 4.18 (q, J = 7.1 Hz, 2H) 1.25 (t, J = 7.0 Hz, 3H).…”

Gold-Catalyzed Partial Hydrogenation of Activated Alkynes Mediated by Triphenylphosphine

“…The mechanism of the partial hydrogenation of activated alkynes mediated by phosphines, has been proposed to proceed through initial attack of the phosphine to the triple bond to form a zwitterionic intermediate that suffers the attack of an oxygen nucleophile (usually water) collapsing in triphenylphosphine oxide and the alkene. 3,4 In our case, we propose that the role of gold is to stabilize the zwitterionic intermediate by coordination with the oxygen of the carbonyl moiety (Scheme 2). Subsequently t-BuOH attacks the atom of phosphonium to form intermediate II that breaks into triphenylphosphine oxide and the Zalkene.…”

“…3 More recently the group of Whittaker reported the reduction of alkynyl carbonyls leading to either the Eor Z-stereoisomers by tuning the reaction conditions. 4 Classical methods to perform the partial hydrogenation of alkynes to alkenes use homogeneous or heterogeneous catalysts under H 2 atmosphere. 5 This process generally delivers the Z-isomer, coming from the syn-addition of H 2 .…”

Copper(I)-Catalyzed Aerobic Oxidation of α-Diazoesters

“…The solvent was removed by rotary evaporation and purified by silica gel column chromatography with petroether/ethyl acetate (50:1) as the eluent to give the desired products 2a – 2n . Compounds 2a – 2c , 2d , 2e , 2f , 2g , 2h – 2i , 2j – 2k , 2l , 2m , 2n , ( Z )- 3 , ( Z )- 4 , and ( E )- 4 are known.…”