title: Regioisomeric and Substituent Effects upon the Outcome of the Reaction of 1-Borodienes with Nitrosoarene Compounds.
abstract: A study of the reactivity of 1-borodienes with nitrosoarene compounds has been carried out showing an outcome that differs according to the hybridization state of the boron moiety. Using an sp(2) boron substituent, a one-pot hetero-Diels-Alder/ring contraction cascade occurred to afford N-arylpyrroles with low to good yields depending on the electronic properties of the substituents on the borodiene, whereas an sp(3) boron substituent led to the formation of stable boro-oxazines with high regioselectivity in most of the cases, in moderate to good yields. (1)H and (11)B NMR studies on two boro-oxazine regioisomers showed that selective deprotection can be performed. Formation of either the pyrrole or the furan derivative is pH- and regioisomer-structure-dependent. The results obtained, together with previous B3LYP calculations, support mechanistic proposals which suggest that pyrrole, or furan, formation proceeds via oxazine formation, followed by a boryl rearrangement and an intramolecular addition-elimination sequence.
authors.affiliation: †Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1, Campus de Beaulieu, CS 74205, 35042 Rennes Cedex, France.|‡Centre for Sustainable Chemical Processes, Department of Chemistry, Durham University, South Road, Durham DH1 3LE, U. K.
authors.forename: Ludovic
authors.initials: L
authors.lastname: Eberlin
authors.affiliation: †Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1, Campus de Beaulieu, CS 74205, 35042 Rennes Cedex, France.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Carboni
authors.affiliation: ‡Centre for Sustainable Chemical Processes, Department of Chemistry, Durham University, South Road, Durham DH1 3LE, U. K.
authors.forename: Andrew
authors.initials: A
authors.lastname: Whiting