Enantiomerically Pure Vinylcyclopropylboronic Esters

Abstract

Keywords: Boron / Cyclopropane / Asymmetric synthesis / Palladium / Natural products Vinylcyclopropanes are versatile intermediates and products in organic synthesis. The corresponding enantiomerically pure boronic esters should lead to highly flexible building blocks with a variety of applications. A detailed study towards the selective synthesis of (E)-and (Z)-vinyl derivatives starting from the known diastereo-and enantiopure cy-

Enantiomerically Pure Cyclopropylamines from Cyclopropylboronic Esters

“…The method of choice was our previously established conversion into the corresponding trifluoroborates 15. [18] Under the reported conditions [KHF 2 (50 equiv. ), MeOH, 80°C] products 15a-c were all obtained in good to excellent yields (Scheme 4, 78-95 %; PG = protecting group).…”

“…It should be noted that methods and reagents commonly used for [a] aminations do not affect boronic acids or esters, but tend to require the intermediacy of more electrophilic boron substrates such as trialkylboranes, borinic acids or dichloroboranes. [17] However, our recent progress with the corresponding trifluoroborates [18] encouraged us to pursue the strategy. We had previously demonstrated that cyclo- propylboronic esters 4 and 5 [19] could indeed be utilised for both routes; [20] here we describe the full details of our findings.…”

Chemical Behaviour of a Prototype Boryl(phosphino)carbene

“…The P1ÀC1 bond length (1.892 (2) ) is in agreement with that reported for PÀC single bonds in phosphinocyclopropanes. [11, 18a] The B1ÀC1 bond is slightly longer than that report-ed for cyclopropylÀB(sp 2 ) linkages (1.52-1.56 ), [19] probably for steric reasons.…”

Enantioselective Synthesis of cis- and trans-Borocyclopropylmethanol: Simple Building Blocks To Access Heterocycle-Substituted Cyclopropylmethanols

“…12 Pinacolate analogues have often been used in borocyclopropanation methodologies. [4][5][6]13 Many of these derivatives are oils and are prone to decomposition through protodeboronation, and are hence recurrently deemed 'unstable' boronic acids. 14 In contrast, cyclopropyltrifluoroborates are solids and display a reduced propensity to undergo protodeboronation, but have limited solubility in moderately polar solvents.…”

“…1 H and 13 C NMR spectra were recorded on Bruker AV400, AV500, and AV700 MHz spectrometers. The corresponding chemical shifts for 1 H NMR and 13 C NMR spectra are recorded in CDCl 3 or acetone-d 6 , and reported in ppm relative to the chemical shift of tetramethylsilane or the residual CHCl 3 ( 1 H:  = 7.26, 13 C:  = 77.2), residual (CD 3 ) 2 CO ( 1 H:  = 2.09, 13 C:  = 205.9), or residual (CD 3 ) 2 SO ( 1 H:  = 2.54, 13 C:  = 40.5) as reference. All 13 C NMR spectra were obtained with complete proton decoupling.…”