Improvement of the reactivity and selectivity of the oxo-Diels–Alder reaction by steric modification of the salen–chromium catalyst
摘要:
Salen-chromium(III) complexes bearing sterically demanding substituents at the 3 and 3' positions are applied for the oxo-Diels-Alder reaction of various aldehydes with Danishefsky's diene. The readily-accessible complex hearing a bulky 3-phenylpent-3-yl substituent revealed its potential affording the cycloadducts With improved reactivity and excellent selectivities up to 96% ee, being considerably superior to the classic Jacobsen's catalyst. (C) 2008 Elsevier Ltd. All rights reserved.
The first example of a chiral Lewis acid-catalyzed enantioselective hetero-Diels-Alder (HDA) reaction between 1-dimethylamino-3-silyloxy-1,3-butadiene (Rawal's diene) and aldehydes is described. The cycloaddition reaction under the influence of 1 mol% of dirhodium(II) tetrakis[N-benzene-fused-phthaloyl-(S)-piperidinonate], Rh(2)(S-BPTPI)(4), proceeded cleanly and gave, after treatment with acetyl chloride