Premium
Radical Cyclisation of α‐Halo Aluminium Acetals: A Mechanistic Study
Author(s) -
Bénéteau Romain,
Boussonnière Anne,
Rouaud JeanChristophe,
Lebreton Jacques,
Graton Jérôme,
Jacquemin Denis,
Sebban Muriel,
Oulyadi Hassan,
Hamdoun Ghanem,
Hancock Amber N.,
Schiesser Carl H.,
Dénès Fabrice
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201504780
Subject(s) - chemistry , propargyl , ring (chemistry) , aluminium , acetal , chemoselectivity , monomer , photochemistry , computational chemistry , stereochemistry , organic chemistry , catalysis , polymer
α‐Bromo aluminium acetals are suitable substrates for Ueno–Stork‐like radical cyclisations affording γ‐lactols and acid‐sensitive methylene‐γ‐lactols in high yields. The mechanistic study herein sets the scope and limitation of this reaction. The influence of the halide (or chalcogenide) atom X (X=Cl, Br, I, SPh, SePh) in the precursors α‐haloesters, as well as influence of the solvent and temperature was studied. The structure of the aluminium acetal intermediates resulting from the reduction of the corresponding α‐haloesters has been investigated by low‐temperature 13 C‐INEPT diffusion‐ordered NMR spectroscopy (DOSY) experiments and quantum calculations, providing new insights into the structures of these thermally labile intermediates. Oxygen‐bridged dimeric structures with a planar Al 2 O 2 ring are proposed for the least hindered aluminium acetals, while monomeric structures seem to prevail for the most hindered species. A comparison against the radical cyclisation of aluminium acetals derived from allyl and propargyl alcohols with the parent Ueno–Stork has been made at the BHandHLYP/6‐311++G(d,p) level of theory, highlighting mechanistic similarities and differences.