title: Reaction of frustrated Lewis pairs with ketones and esters.
abstract: The frustrated Lewis pair (FLP) Mes(2)PCH(2)CH(2)B(C(6)F(5))(2) (1) reacts with an enolizable conjugated ynone by 1,4-addition involving enolate tautomerization to give an eight-membered zwitterionic heterocycle. The conjugated endione PhCO-CH=CH-COPh reacts with the intermolecular FLP tBu(3)P/B(C(6)F(5))(3) by a simple 1,4-addition to an enone subunit. The same substrate undergoes a more complex reaction with the FLP 1 that involves internal acetal formation to give a heterobicyclic zwitterionic product. FLP 1 reacts with dimethyl maleate by selective overall addition to the C=C double bond to give a six-membered heterocycle. It adds analogously to the triple bond of an acetylenic ester to give a similarly structured six-membered heterocycle. The intermolecular FLP P(o-tolyl)(3)/B(C(6)F(5))(3) reacts analogously with acetylenic ester by trans-addition to the carbon-carbon triple bond. An excess of the intermolecular FLP tBu(3)P/B(C(6)F(5))(3), which contains a more nucleophilic phosphane, reacts differently with acetylenic ester examples, namely by O-C(alkyl) bond cleavage to give the {R-CO(2)[B(C(6)F(5))(3)](2)(-)}[alkyl-PtBu(3)(+)] salts. Simple aryl or alkyl esters react analogously by using the borane-stabilized carboxylates as good leaving groups. All essential products were characterized by X-ray diffraction.
authors.affiliation: Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster, Germany.
authors.forename: Bao-Hua
authors.initials: BH
authors.lastname: Xu
authors.forename: Raul Alfonso Adler
authors.initials: RA
authors.lastname: Yanez
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakatsuka
authors.forename: Masato
authors.initials: M
authors.lastname: Kitamura
authors.forename: Roland
authors.initials: R
authors.lastname: Fröhlich
authors.forename: Gerald
authors.initials: G
authors.lastname: Kehr
authors.forename: Gerhard
authors.initials: G
authors.lastname: Erker