Asymmetric Diboration of Terminal Alkenes with a Rhodium Catalyst and Subsequent Oxidation: Enantioselective Synthesis of Optically Active 1,2‐Diols

Abstract

Pin it down: A highly enantioselective diboration of terminal alkenes with chiral 1 and bis(pinacolato)diboron (B2 pin2 ) was realized. Subsequent oxidation of the diboron adducts with sodium peroxoborate readily gave the corresponding optically active 1,2-diols in high yields and high enantioselectivities.

Singular Metal Activation of Diboron Compounds

“…In that case, the use of a base, such as NaO t Bu, accelerated the reaction, and the authors attributed the beneficial influence to the preactivation of the [Rh(III)(OAc) 2 (H 2 O)(Phebox)] complex toward the σ-bond metathesis step. 113 Alternatively, Fernández and Bo demonstrated that Rh(III) complexes modified with NHC ligands could catalyze the diboration of cyclic systems, postulating the oxidative addition of B 2 pin 2 , or bis(neopentylglycolato) diboron (B 2 neop 2 ) to the Rh(III) system as the initial key step (Fig. 5).…”

Catalytic Enantioselective Functionalization of Unactivated Terminal Alkenes

“…73 Use of 1 mol % 19 and 5 mol % NaO t Bu efficiently catalyzed the addition of B 2 pin 2 across an olefin, providing enantiomercially-enriched vicinal 1,2-diols upon oxidation with NaBO 3 . Due to the fact that the reaction is base-promoted, the authors conclude that either σ-bond metathesis or transmetallation is involved in forming a Rh(III)-boryl species from a Rh(III)-O t Bu intermediate, followed by Rh-B bond alkene insertion.…”

Bis(acetato)aqua[2,6-bis[(4S)-4,5-dihydro-4-(1-methylethyl)-2-oxazolyl]phenyl]rhodium

“…However, the use of the unsymmetrical complex 4 improved the yields and enantioselectivities up to 99% (eqs 13 and 14 Aryl-and aliphatic substituted terminal alkenes and dienes were converted to optically active 1,2-diols through the enantioselective diboration and subsequent oxidation in a one-pot manner using the acetate complex 1 and the dimethyl complex 2 (eqs 17 and 18). 16 Allyl ethers and allyl-substituted tertiary amines were also converted to the corresponding diols in high enantioselectivity.…”