ORGN 152 |
Formal insertion of 1,2-dienes into palladacycles with a metal-bonded stereogenic carbon: Synthesis of contiguously substituted 3,4-dihydro-2H-1-benzopyrans
| Genliang Lu and Helena C. Malinakova. Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, 2010 Malott Hall, Lawrence, KS 66045 |
| Palladium-catalyzed reactions exploiting intermolecular carbopalladation of 1,2- or 1,3-dienes followed by an attack of internal nucleophiles on the in situ formed p-allylpalladium complexes have evolved into a powerful synthetic methodology. However, preparation of six-membered rings featuring multiple adjacent stereogenic carbons via this method proved unsuccessful. As a part of our program exploring the chemistry of stable palladacycles with a palladium-bonded stereogenic carbon, we have been investigating reactions between palladacycles I and allenes II. In contrast to catalytic processes, the reactions were expected to proceed via p-allyl intermediates III featuring a nonstabilized, and palladium-bonded ester enolate. Herein we report a systematic study on the effects of steric and electronic nature of substiutents R2 in allenes II on the regio-, diastereo- and enantioselectivity of the formal allene insertion. Allenes II armed with diverse alkyl substituents afforded 3,4-dihydro-2H-benzopyrans IV as major products along with benzopyrans V in 9 : 1 or better regioselectivities. 
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Asymmetric Reactions and Syntheses, Metal-Mediated Reactions, Materials, Molecular Recognition
8:00 PM-10:00 PM, Sunday, August 22, 2004 Pennsylvania Convention Center -- Hall D, Poster
Division of Organic Chemistry
The 228th ACS National Meeting, in Philadelphia, PA, August 22-26, 2004
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