Triple coupling to make alkynes

Stereoselective Synthesis of Unsymmetrical 1,1-Diborylalkenes

“…In 2008, the Walsh group pioneered this ap-proach by reacting Bpin-substituted alkynes with DCB to form UDBA 15. While UDBA 15 was not isolated as a pure compound, it was detected by 11 B NMR spectroscopy with two boron signals at  = 30 ppm and 80 ppm, assignable to Bpin and Cy 2 B (dicyclohexyl boryl), respectively. The more reactive Cy 2 B moiety in 15 was subjected to selective transmetalation with dialkylzinc reagent, leading to the boron/zinc heterobimetallic reagent 16, which further reacted with aldehydes to produce B(pin)-substituted E-allylic alcohols 17 (Scheme 3a).…”

Stereoselective Unsymmetrical 1,1‐Diborylation of Alkynes with a Neutral sp2−sp3 Diboron Reagent

“…To better differentiate the two boryl groups, Masarwa has very recently reported a boron-masking approach to pre-transfer the Bpin at the less steric hindered site of gem-di(Bpin)ethene to BMIDA (MIDA = N-methyliminodiacetic acid) before further functionalization (Scheme 2a). [13] The synthesis of such 1,1-Bpin-BMIDA-ethene has also been reported by Nishihara through a palladium-catalyzed borylation of preprepared ethynyl MIDA boronates. [4j] To circumvent the aforementioned restriction in the boron-differentiation and simplify the boron-masking strategy, a straightforward method and innovative borylation reagents are highly desired to direct equip the olefin with two chemically easily distinguishable boryl groups (Scheme 1b, right).…”

“…Both -Bpin and -BH 2 (NHC) moieties are introduced onto the terminal position of alkynes. In contrast to the boron-masking strategy, which requires the pre-preparation of 1,1-di-(Bpin)alkenes, followed by the introduction of the bulky -BMIDA group trans to the β-substituents, [13] this method offers a one-step synthesis from readily available substrates and enables the synthesis of E-selective UDBAs with the sp 3 boryl being cis to the β-substituents on the olefin. Furthermore, according to the inertness of -BH 2 (NHC) toward oxidants, selective -Bpin oxidation gave acylboranes, whose synthesis is important but challenging.…”

“…Compounds 5, obtained from the two-carbon homologation of UDBAs (R1F), were subsequently converted to substituted Z-stilbenes 13-15, through a one-pot process involving the treatment with N-chlorosuccinimide (NCS), hydrolysis and a palladium catalyzed Suzuki coupling with aryl iodides. [22] Both electron rich and deficient aryl iodides reacted well, leading to R2F products containing nitrile (13), ether (15), as well as amino acid valine ( 14) in 48 %-62 % yields (one purification, two steps from UDBAs) (Scheme 3d, condition A). It is noteworthy that the -Bpin group unexpectedly remained in the Z-stilbenes, after the Deprotonation of the terminal alkyne 2 a-D by potassium tert-butoxide produced the carbanion salt IM1 with the elimination of t BuOD.…”

Stereoselective Unsymmetrical 1,1‐Diborylation of Alkynes with a Neutral sp2−sp3 Diboron Reagent

“…Compounds 5, obtained from the two-carbon homologation of UDBAs (R1F), were subsequently converted to substituted Z-stilbenes 13-15, through a one-pot process involving the treatment with N-chlorosuccinimide (NCS), hydrolysis and a palladium catalyzed Suzuki coupling with aryl iodides. [22] Both electron rich and deficient aryl iodides reacted well, leading to R2F products containing nitrile (13), ether (15), as well as amino acid valine ( 14) in 48 %-62 % yields (one purification, two steps from UDBAs) (Scheme 3d, condition A). It is noteworthy that the -Bpin group unexpectedly remained in the Z-stilbenes, after the [a] Reaction conditions: reactions were conducted with 1 (0.05 mmol, 1.0 equiv), 2 a (0.075 mmol, 1.5 equiv) and base (0.01 mmol, 0.2 equiv) in solvent (0.5 mL) under nitrogen for 12 h. [b] Yields were determined by 1 Deprotonation of the terminal alkyne 2 a-D by potassium tert-butoxide produced the carbanion salt IM1 with the elimination of t BuOD.…”