Asymmetric synthesis of acetamido boronic acids and asymmetric synthesis using boronic esters.

摘要

((1{dollar}R{dollar})-1-Acetamido-3-(methylthio)propyl) boronic acid, the boronic acid analogue of {dollar}N{dollar}-acetyl- scL-methione, has been synthesized and the structure of its ethylene glycol ester has been determined by X-ray diffraction. ({dollar}S{dollar})-Pinanediol ethenylboronate was homologated with (dichloromethyl)lithium to yield (chloroallyl)boronate, which was converted to the silylated amino derivative with lithiohexamethyldisilizane. Desilylation and acetylation followed by a radical addition of methanethiol gave crystalline ({dollar}S{dollar})-pinanediol ((1{dollar}R{dollar})-1-acetamido-3-(methylthio)propyl) boronate. Pinanediol was cleaved by boron trichloride to give the free acetamido boronic acid which was converted to its crystalline ethylene glycol ester. The X-ray structure indicates that the acetamido oxygen atom is coordinated to the slightly acidic boron atom and the 1,3,2-dioxaborolane ring is nonplanar.; (1{dollar}R{dollar})-1-Acetamido-2-phenylethyl-1-boronate-1-{dollar}sp{lcub}13{rcub}{dollar}C, the boronic acid analogue of {dollar}N{dollar}-acetylphenylalanine, has been synthesized by a known route utilizing an excess of (dichloromethyl)lithium, but here it has been found that a stoichiometric amount of (dichloromethyl)lithium will suffice in the reaction scheme. The {dollar}sp1{dollar}H and {dollar}sp{lcub}13{rcub}{dollar}C NMR data are given for the intermediates and the final product.; A new and efficient synthesis of (3{dollar}S{dollar},4{dollar}S{dollar})-2,5-dimethoxy-2,5-dimethyl-3,4-hexanediol has been developed and its uses as a chiral director for chain extension of boronic esters are described.; The reaction of {dollar}tert{dollar}-butyl {dollar}trans{dollar}-lithiopropionate with various {dollar}alpha{dollar}-halo boronic esters is examined. The lithium enolate reacts with ({dollar}S,S{dollar})-diisopropylethanediol (1{dollar}R{dollar})-(1-bromopentyl)boronate and yields {dollar}tert{dollar}-butyl (2{dollar}S{dollar},3{dollar}S{dollar})-3-hydroxy-2-methylheptanoate in a 60:1 threo:erythro ratio. Various other threo:erythro ratios are established for different chiral directors of the boronic esters and different substrates that are attached to the boronic esters.; The displacement of chloride ion for ({dollar}S{dollar})-pinanediol (chloroallyl)boronate with various oxygen nucleophiles is examined. The reaction of ({dollar}S{dollar})-pinanediol (chloroallyl)boronate and the thermodynamic lithium enolate of 2-methylcyclohexanone undergoes a Cope-type rearrangement and a competing Sn2{dollar}spprime{dollar} reaction in a 60:40 enantiomeric excess at the chiral quaternary center with a {dollar}trans{dollar} double bond {dollar}alpha{dollar} to the boron atom.