Synthesis of 1,1‐Diborylalkenes through a Brønsted Base Catalyzed Reaction between Terminal Alkynes and Bis(pinacolato)diboron

Abstract

Abstract:A new method for the synthesis of 1,1-diborylalkenes through a Brønsted-base-catalyzed reaction between terminal alkynes and bis(pinacolato)diboron has been developed. The protocol allows direct synthesis of functionalized 1,1-diborylalkenes from various terminal alkynes including propiolates, propiolamides and 2-ethynylazoles.

Cobalt-Catalyzed 1,1-Diboration of Terminal Alkynes: Scope, Mechanism, and Synthetic Applications

“…In 2015, Sawamura and co-workers reported the direct preparation of 1,1-diborylalkenes from terminal alkynes and B 2 Pin 2 using LiO t -Bu as the catalyst (Scheme 2A). 13 While effective and an important advance, this reaction is limited to alkynes bearing electron-withdrawing substituents such as propiolates.…”

Copper‐Catalyzed Triboration of Terminal Alkynes Using B2pin2: Efficient Synthesis of 1,1,2‐Triborylalkenes

“…[2a, 15] The first metalcatalyzed diboration of alkynes was reported by Suzuki and Miyaura in 1993 using a Pt catalyst, [16] and significantly improved Pt catalyst systems were reported by our group. [17] During the last few years, Pd, [18] Cu, [19] Co, [11c, 20] Fe, [21] Zn, [14x] and metal-free [22] systems were reported for the diboration of alkynes, which provide practical and economic alternatives to the Pt-catalyzed processes (Scheme 2 b). [16][17]23] However, the availability of diverse multiborylalkenes is quite limited because of the lack of efficient and versatile synthetic methods.…”

Access to 1,1‐Diborylalkenes and Concomitant Stereoselective Reactivity

“…In 2015 Ohmiya and Sawamura reported the 1,1‐diboration of triple carbon–carbon bonds with B 2 pin 2 . Activated terminal alkynes were selected to probe this new concept, including those containing a propiolate, a propiolamide or a imidazole substituent (Scheme a–c).…”

“…This is the case in Suzuki–Miyaura coupling between the β,β‐diborylacrylate shown in Scheme and bromobenzene in the presence of a Pd(OAc) 2 catalyst precursor modified with DtBPF [DtBPF = 1,1′‐bis(di‐ tert ‐butylphosphanyl)ferrocene] and K 3 PO 4 as a base. Sawamura and co‐workers demonstrated that the cross‐coupling occurs selectively at the boron site trans to the ester group to give the corresponding alkenylboronate (with E/Z > 99:1) in high yield (Scheme ) . This stereoselectivity is probably due to the steric character of the ester group.…”

“…Sawamura and co‐workers found that β,β‐diborylacrylate compounds can be efficiently transformed into the corresponding geminal diborylalkanes through copper‐catalyzed conjugate reduction with poly(methylhydrosiloxane) (PMHS, Scheme a). The reaction requires a copper(I) catalytic system formed in situ from CuCl and the N‐heterocyclic carbene ligand IPr, along with added NaO t Bu/ t BuOH .…”