title: Diels-Alder Reactions of 1,2-Azaborines.
abstract: Diels-Alder reactions employing 1,2-azaborine heterocycles as 1,3-dienes are reported. Carbocyclic compounds with high stereochemical and functional complexity are produced, as exemplified by the straightforward two-step synthesis of an amino allyl boronic ester bearing four contiguous stereocenters as a single diastereomer. Whereas electron-deficient dienophiles undergo irreversible Diels-Alder reactions, a reversible Diels-Alder reaction with the less electron-deficient methyl acrylate is observed. Both the N and the B substituent of the 1,2-azaborine exert significant influence on the [4+2] cycloaddition reactivity as well as the aromatic character of the heterocycle. The experimentally determined thermodynamic parameters of the reversible Diels-Alder reaction between 1,2-azaborines and methyl acrylate correlate with aromaticity trends and place 1,2-azaborines approximately between furan and thiophene on the aromaticity scale.
authors.affiliation: Department of Chemistry, Boston College, Chestnut Hill, MA 02467 (USA).
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Burford
authors.affiliation: Department of Chemistry, Boston College, Chestnut Hill, MA 02467 (USA).
authors.forename: Bo
authors.initials: B
authors.lastname: Li
authors.affiliation: Department of Chemistry, The University of Alabama, Tuscaloosa, AB 35487 (USA).
authors.forename: Monica
authors.initials: M
authors.lastname: Vasiliu
authors.affiliation: Department of Chemistry, The University of Alabama, Tuscaloosa, AB 35487 (USA).
authors.forename: David A
authors.initials: DA
authors.lastname: Dixon
authors.affiliation: Department of Chemistry, Boston College, Chestnut Hill, MA 02467 (USA). shihyuan.liu@bc.edu.
authors.forename: Shih-Yuan
authors.initials: SY
authors.lastname: Liu
keywords: aromaticity; azaborine heterocycles; boron; cycloaddition; synthetic methods