Synthesis of Secondary and Tertiary Alkylboranes via Formal Hydroboration of Terminal and 1,1-Disubstituted Alkenes

Abstract

Copper-catalyzed functionalization of terminal or 1,1-disubstituted alkenes with bis(pinacolato)diboron and methanol provides formal hydroboration products with exceptional regiocontrol favoring the branched isomer. Through pairing this procedure with photocatalytic cross couplings using iridium and nickel co-catalysis, an effective, highly regiose-lective procedure for the hydroarylation of terminal alkenes is provided.

Recent Advances in Hydrometallation of Alkenes and Alkynes via the First Row Transition Metal Catalysis

“…[90] Scheme 28 Cu-B catalyzed enantioselective hydroboration of alkenylsilanes Using the privileged chiral bisphosphine ligand [(R)-DTBMsegphos (4)], Tortosa and co-workers disclosed a copper-catalyzed diastereo-and enantioselective hydroboration of cyclopropenes, providing enantiomerically enriched cyclopropylboronates with a quaternary stereocenter (Scheme 29a). [94,95] More recently, Shi and co-workers developed a sterically hindered chiral NHC ligand [(R,R,R,R)-ANIPE, 30] for the copper-catalyzed asymmetric hydroboration of unactivated terminal alkenes, providing an expedient to access chiral alkylboronic esters with good regioselectivity and excellent enantioselectivity (Scheme 30c). [92] Scheme 29 Phosphine-CuBpin catalyzed enantioselective hydroboration of cyclopropenes and 1,1-diaryl alkenes The hydroboration of unactivated alkenes was also facilitated via the Cu-B mediated methodology, Ito and co-workers reported an anti-Markovnikov type process with Xantphos (9) as the ligand (Scheme 30a), [93] as well as a Markovnikov type reaction with a bulky bisphosphine ligand (29) (Scheme 30b).…”

Copper‐Catalyzed Enantioselective Markovnikov Protoboration of α‐Olefins Enabled by a Buttressed N‐Heterocyclic Carbene Ligand

“…[9] As illustrated in the proposed catalytic cycle (Figure 1b Abulky ligand would facilitate the selective formation of Ca by avoiding the steric interaction between the ligand and the alkene substituent as shown in Cb.Subsequent protonation of the transient alkylcopper species D with an alcohol as the proton donor would furnish the chiral protoboration product E and release the copper alkoxide F.As-metathesis reaction between F and the diboron reagent G would regenerate A and close the catalytic cycle.T he regio-and enantiocontrol of the olefin borylcupration step is the key event that determines the regio-and stereochemical outcome of the transformation. However,d espite recent advances in copper-catalyzed protoboration [10] and boro-functionalization [11] of a-olefins,a n efficient enantioselective Markovnikov protoboration of aolefins has yet to be reported. [12] We sought ab ulky chiral ligand with ahigh level of regiocontrol for borylcupration yet capable of effectively discerning the well-remoted small steric difference between the prochiral faces of the terminal alkenes.…”

Enantioselective Rhodium(III)-Catalyzed Markovnikov Hydroboration of Unactivated Terminal Alkenes

“…Although aliphatic terminal alkenes usually give the linear alkylboronic ester, 10 recently disclosed copper-catalyzed hydroboration processes, employing bulky phosphine or NHC ligands, give the branched Markovnikov product. 11,12 The process, however, has yet to be rendered asymmetric. A general catalytic asymmetric method for the generation of secondary alkylboronic esters from the abundant feedstock of aliphatic terminal alkenes 13 remains an unmet challenge, which is now addressed in this paper.…”