Copper(I)‐Catalyzed Highly Regio‐ and Stereoselective Boron Addition–Protonolysis of Alkynamides to give Alkenamides

Abstract

Copper‐catalyzed and highly chemoselective reduction of N‐alkynylamides by a boron addition–protonolysis protocol is presented. The reaction proceeds with the addition of boryl‐copper complex to N‐alkynylamides with high regioselectivity and stereoselectivity, followed by regiocontrolled transmetallation of the α‐site of the alkenylboronate with MeOCuL to afford N‐alkenylamides in good yields. Deuterium labeling experiments indicated that both of the alkenyl hydrogen atoms originate from the additive methanol.

Studies on copper(i)-catalyzed highly regio- and stereo-selective hydroboration of alkynamides

“…The experimental results showed that the reactions with PPh 3 , P(Bu-n) 3 and P(OEt) 3 gave no desired α-site regiocontrolled alkenamide boronate (Z)-2a, but the mixture of the β-site regio-isomer (Z)-3a and semi-reduced alkenamide (Z)-4a (entries 1-3). 16 When SPhos or XPhos was selected as the ligand of the present system, the reaction only afforded (Z)-2a in very poor yields, and the corresponding regio-and chemo-selectivity were not satisfactory (entries 4-5). Surprisingly, in the case of LB-Phos•HBF 4 , 17 the yield of the Cu(I)-catalyzed hydroboration reaction could be dramatically increased to 84% with good reactivity and selectivity (entry 6).…”

“…15 In previous studies, we have demonstrated that aryl-and TMS-substituted alkynamides could be cata-lytically reduced to (Z)-alkenamides with high stereoselectivity by the boron addition-protonolysis protocol. 16 Herein, we report the copper(I)-catalyzed highly regio-and stereo-selective hydroboration of alkynamides and further elaboration of products.…”

Preparation and Utility of N-Alkynyl Azoles in Synthesis

“…In 2000, Bauld and Gao published the reduction of N -ethynyl carbazole with lithium aluminum deuteride forming N -( cis -2-deuteriovinyl)carbazole ( 213 ) (Scheme 57, Reaction (2) [87]). In contrast to the stereoselectivity of this transformation, Swamy reported in 2017 that the H-transfer reduction of N -alkynyl carbazole 214 affords a mixture of ( E )- and ( Z )-products 215 (Scheme 57, Reaction (3)), despite the highly ( E )-selective reduction of N -alkynyl amides under these conditions [88].…”

Convenient and Practical Alkynylation of Heteronucleophiles with Copper Acetylides

“…13 Characterization data were consistent with those reported in the literature. 14 -1-yn-1-yl)oxazolidin-2-one (4h) Prepared according to procedure 2 from oct-1-yn-1-ylcopper (2b; 1.9 g, 11.2 mmol), oxazolidin-2-one (3.9 g, 44.8 mmol), and TMEDA (1.7 mL, 11. Characterization data were consistent with those reported in the literature.…”