He was an extraordinary mentor, scholar, and friend who left a huge empty orbital in all of us who knew him.

We report a transition-metal-free trans-selective semireduction of alkynes with pinacolborane and catalytic potassium tertbutoxide. A variety of 3-substituted primary and secondary propiolamides, including an analog of FK866, a potent nicotinamide mononucleotide adenyltransferase (NMNAT) inhibitor, are reduced to the corresponding (E)-3-substituted acrylamide derivatives in up to 99% yield with >99:1 E/Z selectivity. Mechanistic studies suggest that an activated Lewis acid−base complex transfers a hydride to the αcarbon followed by rapid protonation in a trans fashion.T he semireduction of an alkyne to a (Z)-or (E)-alkene is fundamental in organic synthesis. Methods toward the (Z)-selective semireduction of alkynes are well established, 1 with the most popular being semihydrogenation mediated by Lindlar's catalyst (Pd/CaCO 3 /Pb/quinoline). 2 The complementary reduction methods affording (E)-alkenes are limited. Early work involved treating alkynes with dissolved metals, 3 low-valent chromium salts, 4 or metal hydrides; 5 however, these methods are harsh and highly substrate-dependent. Trost and coworkers later developed a general method for the (E)selective semireduction of alkynes via a ruthenium-mediated hydrosilylation, which is subsequently protodesilylated with TBAF, affording (E)-alkenes in high yield with excellent stereoselectivity. 6 Similarly, Furstner developed a one-step, stereoselective semireduction of alkynes using a similar ruthenium catalyst. 7 Beyond these two examples, various transition-metal-catalyzed methods toward the (E)-selective semireduction of alkynes have been developed, such as Pd, 1i,n,8 Rh, 9 Ru, 1q,10 In, 11 Ir, 1ab,12 Co, 1ac,13 Ni, 1ad,14 and Fe 15 (Scheme 1A).The transition-metal-free semireduction of alkynes to (E)alkenes is limited to a few examples. Koide treated γ-hydroxyα,β-alkynoic esters with Red-Al or NaBH 4 and obtained alkenoic esters in good yield with good stereoselectivity, although the substrate scope is limited by the necessity of the directing ability of the γ-hydroxyl moiety (Scheme 1B). 16 Chen and Liu employed sodium sulfide nonahydrate as a reducing reagent to facilitate the stereoselective semihydrogenation of diarylalkynes to (E)-alkenes (Scheme 1C). This method successfully reduced a broad scope of diarylalkynes in good to excellent yield with high stereoselectivity (98:2 E/Z). 17 Similarly, Zhou and Liu demonstrated the semireduction of diarylalkynes utilizing H 2 Se, which was generated in situ from Se/DMF/H 2 O (Scheme 1C), to obtain alkenes in good yield with high stereoselectivity (>95:5 E/Z). 18 However, both aforementioned methods were limited to diarylalkynes, and the reaction conditions were fairly harsh. Recently, our group

A method for the preparation of air stable difluoroboryl acrylamides is reported. In contrast to the ubiquitous organotrifluoroborate salts, difluoroboryl acrylamides are relatively nonpolar and are readily purified by silica chromatography. Difluoroboryl acrylamides serve as efficient substrates in cross-coupling reactions to afford the corresponding trisubstituted acrylamides in good to excellent yields. The utility of the difluoroboryl group in various chemical transformations is presented.

We report a chemoselective, phosphine-catalyzed semireduction of primary and secondary propiolamides. In the presence of stoichiometric pinacolborane and catalytic n-tributylphosphine, a variety of propiolamides were successfully converted to the corresponding acrylamides in excellent yield with (E)stereoselectivity. The reaction condition is tolerant of various functional groups including alkene, alkyne, ketone, or ester. Deuterium labeling studies established that the hydride from activated pinacolborane is added to the α-carbon and the proton on the amide nitrogen is abstracted by the ß-carbon to furnish the (E)acrylamides. DFT calculations revealed a clear energetic driving force for the (E)-over the (Z)-isomer.

A highly efficient regio- and stereoselective method for allenoate borylation has been developed. Using CuCl and bis(pinacolato)diboron in methanol, a variety of allenoates underwent beta boration, α-protonation to afford the...