Regio‐ and Stereoselective Chan‐Lam‐Evans Enol Esterification of Carboxylic Acids with Alkenylboroxines

Abstract

Efficient and scalable Cu(II)-mediated enol esterification methodology of carboxylic acids from alkenyl boroxines and boronic acids is presented. The reaction shows a wide scope in aliphatic and aromatic carboxylic acids in combination with several alkenyl boroxines. In the case of 2-substituted alkenyl boroxines the double bond configuration was fully retained in the enol ester product. Also N-hydroxyimides and imides could be transformed in the respective amidooxy vinyl enol ethers and vinyl enamides. Finally, with the exception of methionine, all other 19 canonical amino acids showed their compatibility to give the enol esters in a stereoselective fashion.

Dual Activity of Grubbs-Type Catalyst in the Transvinylation of Carboxylic Acids and Ring-Closing Metathesis Reactions

“…The product was isolated as an yellow oil from a silica column eluted by EtOAc/hexanes (1:10) in 86% yield (56 mg); 1 H NMR (400 MHz, CDCl 3 ): δ 7.29–7.21 (m, 5H), 7.18 (t, J = 3.2 Hz, 1H), 4.83 (dd, J = 13.9, 1.7 Hz, 1H), 4.52 (dd, J = 6.3, 1.7 Hz, 1H), 3.63 (s, 2H); 13 C­{H} NMR (100 MHz, CDCl 3 ): δ 168.7, 141.3, 129.3, 128.7, 127.3, 98.0, 40.9. The 1 H and 13 C NMR data were in accordance with those reported in the literature …”

Palladium Catalyzed Direct Carbonylative Thiomethylation of Aryldiazonium Salts and Amines with 4-(Methylthio)-2-Butanone as (Methylthio) Transfer Agent

“…97, 144.01, 134.59, 129.19, 127.15, 21.58, 11.55. GC-MS (EI, 70 ev) m/z (%) = 166 (M + , 8), 119 (100), 91 (55), 65 (21), 51 (4).…”

“…13 C NMR (151 MHz,CDCl 3 ) δ 190.91,162.12,155.48,131.64,130.01,129.25,124.58,120.11,117.33,11.62. GC-MS (EI, 70 ev) m/z (%) = 244 (M + , 6), 197 (100), 141 (18), 115 (21), 77 (17), 51 (9).…”

Stereoselective C-terminal peptide elongation from Chan–Lam–Evans reaction generated isopropenyl esters

“…Recently, we disclosed the efficient enol esterification of carboxylic acids via the CLE reaction and demonstrated the compatibility with all proteogenic amino acids, except methionine. 10 Furthermore, no racemisation of the C-terminus was observed during the CLE-type enol esterification of amino acids. This prompted us to study the possibility of stereoselective elongation of peptides at the C-terminus employing isopropenyl esters as mild activating groups.…”

“…Because we have shown earlier the compatibility of the CLE-reaction with appropriately protected canonical amino acids, we aimed at a limited but representative set of target tripeptides. 10 As the C-and N-terminal residues Gly, Ala, Phe and Val, representing a gradual increase in steric hindrance, were selected of which the outcome may be extrapolated to the other canonical amino acids. 17 At the C-terminus also the D-configured analogs were included to allow precise HPLC-analysis to determine the stereointegrity of the aminolysis reaction.…”