title: Lewis acid-base 1,2-addition reactions: synthesis of pyrylium borates from en-ynoate precursors.
abstract: Treatment of methyl (Z)-2-alken-4-ynoates with the strong Lewis acid tris(pentafluorophenyl) borane, B(C6F5)3, yield substituted zwitterionic pyrylium borate species via an intramolecular 6-endo-dig cyclisation reaction.
authors.affiliation: School of Chemistry, Main Building, Cardiff University, Cardiff CF10 3AT, Cymru/Wales, UK. melenr@cardiff.ac.uk.
authors.forename: Lewis C
authors.initials: LC
authors.lastname: Wilkins
authors.affiliation: School of Chemistry, Main Building, Cardiff University, Cardiff CF10 3AT, Cymru/Wales, UK. melenr@cardiff.ac.uk.
authors.forename: Hugh B
authors.initials: HB
authors.lastname: Hamilton
authors.affiliation: School of Chemistry, Main Building, Cardiff University, Cardiff CF10 3AT, Cymru/Wales, UK. melenr@cardiff.ac.uk.
authors.forename: Benson M
authors.initials: BM
authors.lastname: Kariuki
authors.affiliation: Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany and Chemistry Department, Faculty of Science, King Abdulaziz University (KAU), Jeddah 21589, Saudi Arabia.
authors.forename: A Stephen K
authors.initials: AS
authors.lastname: Hashmi
authors.affiliation: Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
authors.forename: Max M
authors.initials: MM
authors.lastname: Hansmann
authors.affiliation: School of Chemistry, Main Building, Cardiff University, Cardiff CF10 3AT, Cymru/Wales, UK. melenr@cardiff.ac.uk.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Melen