A mechanistic study of the Lewis base-directed cycloaddition of 2-pyrones and alkynylboranes.
Significant rate enhancements in the Diels-Alder reaction of alkynes and 2-pyrones bearing a Lewis basic group are observed when a combination of alkynyltrifluoroborates and BF3·OEt2 is used. This process generates functionalized aromatic compounds with complete regiocontrol. The observed rate enhancement was studied by density functional theory methods and appears to originate from coordination of the diene substrate to a mixture of alkynylborane intermediates, followed by a Lewis acid-mediated product equilibration step. Evidence for this mechanism is presented, as is the enhanced promotion of the cycloaddition via the use of alternative Lewis acid promoters.
Department of Chemistry, University of Sheffield , Sheffield S3 7HF, U.K.
Damien F P
DF
Crépin
Joseph P A
JP
Harrity
Julong
J
Jiang
Anthony J H M
AJ
Meijer
Anne-Chloé M A
AC
Nassoy
Piotr
P
Raubo
D000480:Alkynes / Q000737:chemistry*; D001880:Boranes / Q000737:chemistry*; D003500:Cyclization; D058115:Lewis Bases / Q000737:chemistry*; D015394:Molecular Structure; D011753:Pyrones / Q000737:chemistry*; D011789:Quantum Theory
C584017:2-pyrone; D000480:Alkynes; D001880:Boranes; D058115:Lewis Bases; D011753:Pyrones