Stereochemical Control via Chirality Pairing: Stereodivergent Syntheses of Enantioenriched Homoallylic Alcohols

Abstract

We report herein the development of stereodivergent syntheses of enantioenriched homoallylic alcohols using chiral nonracemic a-CH 2 Bpin-substituted crotylboronate.C hiral phosphoric acid (S)-A-catalyzed asymmetric allyl addition with the reagent gave Z-anti-homoallylic alcohols with excellent enantioselectivities and Z-selectivities.W hen the enantiomeric acid catalyst (R)-A was utilized,t he stereoselectivity was completely reversed and E-anti-homoallylic alcohols were obtained with high E-selectivities and excellent enantioselectivities.B ypairing the chirality of the boron reagent with the catalyst, two complementary stereoisomers of chiral homoallylic alcohols can be obtained selectively from the same boron reagent. DFT computational studies were conducted to probe the origins of the observed stereoselectivity.T hese reactions generate highly enantioenriched homoallylic alcohol products that are valuable for rapid construction of polyketide structural frameworks.

An overview of the applications of chiral phosphoric acid organocatalysts in enantioselective additions to CO and CN bonds

“…In their most recent reports, Chen and co-workers describe allylboration reactions using enantioenriched CH 2 Bpin substituted E -crotylboronate. 336 Curiously, in this case, the absolute configuration of the CPA-catalyst allows controlling the E / Z selectivity of the reaction, providing access to a wide variety of new chiral alcohols with high stereocontrol. Moreover, the authors illustrated the applicability of their method to the synthesis of ACRL toxin IIIB.…”

Site-Selective Functionalization of C(sp3) Vicinal Boronic Esters

“…The same group has described another asymmetric approach to these reactions. 40 Thus, using each of the enantiomers of a chiral phosphoric acid based on binol as acidic catalysts, (S)-A and (R)-A, the addition of (S)-α-borylmethyl-(E)-crotylboronate to aldehydes was stereodivergent, yielding after oxidation (4S,5S,Z)-and (4R,5R,E)-diols, respectively (Scheme 30). A formal synthesis of ACRL Toxin IIIB has been accomplished using this methodology from (R)-α-borylmethyl-(E)-crotylboronate and an α,β-unsaturated aldehyde.…”

“…The same group has described another asymmetric approach to these reactions . Thus, using each of the enantiomers of a chiral phosphoric acid based on binol as acidic catalysts, ( S )- A and ( R )- A , the addition of ( S )-α-borylmethyl-( E )-crotylboronate to aldehydes was stereodivergent, yielding after oxidation (4 S ,5 S , Z )- and (4 R ,5 R , E )-diols, respectively (Scheme ).…”

Synthesis of α-Borylmethyl-(E)-allylborons via Cu-Catalyzed Diboration of 1-Substituted Allenols and Their Application in Stereoselective Aldehyde Allylation

“…Moreover, this method required a rare and expensive precatalyst, PdG3. Recently, Chen and co-workers , reported the synthesis of class IV reagents via the Pt-catalyzed enantioselective diboration of 1,4-pentadiene (Morken protocol), followed by Ru (Grotjahn protocol) or Ni catalysis (Hilt protocol) for ( E )- or ( Z )-selective olefin isomerization (Scheme d) . However, it was applied only to the synthesis of α-borylmethyl-( E )- or α-borylmethyl-( Z )-crotylborons.…”