Regioselective Spiroannulations of α‐Acetyl Lactones

Abstract

Monocyclic spiroannulation precursors 3a−c were obtained by Michael reactions of α-acetyl lactones 6a−c with methyl vinyl ketone (7). The selective formation of either regioisomer of both β-oxo (5a−c) and δ-oxo (4a−c) lactones from 3a−c was achieved by varying the reaction conditions. The δ-oxo lactones 4a−c were obtained under basic (buffered) conditions in a pyrrolidine/AcOH system. Under acidic con-

Regioselective Enamine Formation from Oxonia‐Boranuida‐Betaines and Their Application in Asymmetric Michael Reactions

“…Cyclization under standard Robinson conditions (pyrrolidine, glacial acetic acid) [14] afforded the δ-oxolactam 12, being the ''wrong'' regioisomer (Scheme 6). The constitution of 12 was established by the 3 J( 1 H, 13 C) correlation of the methyl protons to the spiro carbon atom in a 2D-1 H, 13 C NMR experiment.…”

The diketo form of (+)-(1R,4R)-3-benzoylcamphor

“…The Ce III -catalysed -hydroxylation of -diketo compounds with molecular oxygen is a mild atom-economic and environmentally friendly method for the synthesis of the biologically important -hydroxy--dicarbonyl group (Christoffers & Werner, 2002;Christoffers et al, 2003Christoffers et al, , 2004Rö ssle et al, 2004). The structure determination of the title compound, (I), was performed as a part of a project on the preparation of well defined chiral metal camphorates (Niemeyer & Gan, 2005;Seo and Niemeyer, 2006) which might be used for enantioselective oxidation reactions.…”

trans-Bis[(+)-(1R,4R)-3-benzoylcamphorato-κ2O,O′]copper(II)

“…The Ce III -catalysed -hydroxylation of -diketo compounds with molecular oxygen is a mild atom-economic and environmentally friendly method for the synthesis of the biologically important -hydroxy--dicarbonyl group (Christoffers & Werner, 2002;Christoffers et al, 2003Christoffers et al, , 2004Rö ssle et al, 2004). The structure determination of the title compound, (I), was performed as part of a project on the preparation of well defined chiral metal camphorates (Niemeyer & Gan, 2005; which might be used for enantioselective oxidation reactions.…”