The Anti-Selective Boron-Mediated Asymmetric Aldol Reaction of Carboxylic Esters

Unprecedented 8,9′-Neolignans: Enantioselective Synthesis of Possible Stereoisomers for Structural Determination

“…These 8,9′-neolignans may be biosynthesized by the following reaction sequences (Scheme 4): (1) dimerization of coniferyl alcohols (19) through bond formation between conjugated anion species 20, generated by the deprotonation of a phenolic hydrogen, and vinylogous quinone methide 21, produced by dehydration at the C-8 and the C-9 positions; (2) syn-selective hydration of the C−C bonded dimer 22; (3) prenylation; and (4) stereospecific cyclization to form the (S)-2-(1,1-dimethyl-1-hydroxymethyl)dihydrobenzofuran skeleton. The possible presence of structurally related dimeric phenylpropanoids, such as demethoxy-congeners of 3, has been identified in this plant source, although they are not yet fully characterized.…”

Practical asymmetric synthesis of β-hydroxy γ-amino acids via complimentary aldol reactions

“…Many research programs have focused on the anti -aldol reaction. 24 Abiko and co-workers had demonstrated that norephedrine propionates 3b could be utilized with dicyclohexylboron triflate to provide 1,2- anti aldol products in good diastereomeric excess and yield. Aspiring towards the goals of high chemical efficiency, selectivity, operational simplicity and maximum material throughput, we initiated our studies with the Abiko protocol.…”

“…Initially a solution of dicyclohexylboron triflate in hexanes (1 M) was employed as reported by Abiko. 24d Further studies revealed dichloromethane as a superior solvent for this reaction (Scheme 3). The anti- aldol reactions performed with a dichloromethane solution (1 M) of dicyclohexylboron triflate were faster, higher yielding, and more consistent.…”

Design and synthesis of a potential SH2 domain inhibitor bearing a stereodiversified 1,4-cis-enediol scaffold

“…1,4- cis -enediol compounds 1 can be made by coupling a protected chiral alkyne and Weinreb amide. The alkyne can in turn be synthesized by Evans syn 16 or Masamune anti 17 stereocontrolled aldol coupling of TMS-propynal with the appropriate homobenzyl substituted chiral auxiliary. Herein we describe the synthesis of the ( R,R,R )-stereoisomer.…”