Ligand-free, catalytic and regioselective hydroboration of selenoalkynes

Abstract

The copper-catalyzed hydroboration of selenoalkynes in a regio- and stereoselective fashion is reported, delivering selenium-containing vinylboronate products in good yields. The reported protocol fills an important gap in the literature...

Overview of Regioselective and Stereoselective Catalytic Hydroboration of Alkynes

“…Cu catalysts have contributed significantly to hydroboration of alkynes in a highly stereo‐ and regioselective manner [63–77] . It is worthy of mention that the β‐ or α‐selective borylation of aromatic substituted unsymmetrical internal alkynes (such as 32 or 34 ) was achieved by varying the borylating reagents.…”

“…[38,39] The 3d transition metals are earth-abundant and demonstrate less toxic behavior, which makes them one of the prior choices for catalysis. In this regard, various first-row transition metals are also used as efficient catalysts in syn-selective hydroboration, for instance, Ti, [48,49] Mn, [50] Fe, [51][52][53][54][55][56][57][58] Co, [59][60][61] Ni, [62] Cu, [63][64][65][66][67][68][69][70][71][72][73][74][75][76][77] and Zn. [78] One of the early reports of regio-and stereoselective hydroboration of 1-(alkylthio)-1-alkyne (28) using HBcat and NiCl 2 (dppe) as catalysts (Scheme 8) was published by Miyaura and Suzuki in 1993.…”

“…[49,79] Cu catalysts have contributed significantly to hydroboration of alkynes in a highly stereo-and regioselective manner. [63][64][65][66][67][68][69][70][71][72][73][74][75][76][77] It is worthy of mention that the β-or α-selective borylation of aromatic substituted unsymmetrical internal alkynes (such as 32 or 34) was achieved by varying the borylating reagents. The Yun, Tsuji, and Cazin groups independently reported a similar Cu-catalytic system using B 2 pin 2 as the borylating precursor to achieving β-selective synhydroboration products 33 β or 35 β (Scheme 10).…”

“…[71] Chalcogensubstituted alkynes also control the regioselectivity of a syn-hydroboration reaction (as shown in 44-46 and 48). [67,68,73] Given the importance of selective hydroboration reactions and considering the high efficacy of the copper catalytic system, a few heterogeneous Cucatalytic systems have been reported in the hydroboration of alkynes with high syn-selectivity. [66,72,76] Bearing in mind the importance of earth-abundant metal catalysts in selective hydroboration reactions, Fe-based complexes have been widely studied.…”

Synthesis of Tri‐ and Tetrasubstituted Alkenyl Boronates from Alkynes

“… [40] Analogous selenoalkynes afforded exclusively the β isomer of the vinylboronates (Scheme 20). [63a] Even a ligand free protocol based solely on CuCl, NaOH and methanol was efficient for the hydroboration of internal selenoalkynes to afford β‐seleno vinylboronates [63b] …”