Asymmetric Hydrovinylation of 1-Vinylcycloalkenes. Reagent Control of Regio- and Stereoselectivity
摘要:
1-Vinylcycloalkenes undergo highly regio- and enantioselective (>98% ee) 1,4-hydrovinylation (HV) when treated with ethylene (1 aim) at room temperature in the presence of [(S,S)-2,4-bis-diphenylphosphinopentane (BDPP)]CoCl2 (0.05 equiv) and methylaluminoxane. The minor 1,2-HV products, seen only in 1-vinylcyclohexene (similar to 15%) and 1-vinylcycloheptene (2%), are formed as racemic mixtures. The corresponding Ni(II)-catalyzed HV reactions of these substrates give mostly the 1,2-adducts. Racemic 4-tert-butyl-1-vinylcyclohexene, when treated with Co[(S,S)-(BDPP)]Cl-2 and ethylene, undergoes a rare enantiodivergent reaction giving two diastereomers each in >98% cc.
An Improved Synthesis of 5-Ethenyl-4a-methyl-2-oxo-2,3,4,4a,7,8-hexahydronaphthalene and Similar 1,3-Dienes using Palladium Catalyzed Cross-Coupling Methodology
作者:Kollol Pal
DOI:10.1055/s-1995-4148
日期:1995.12
We report an efficient synthesis of 1,3-dienes from readily available enol triflates and vinyltributyltin using Pd2(dba)3 and triphenylarsine. Our approach allows for the preparation of these systems at room temperature and thus prevents isomerization to other isomeric dienes. The mild reaction conditions are attributed to the rate acceleration of the cross-coupling reaction due to the weak Ï-donation of the triphenylarsine ligand on the palladium catalyst.
Cascade reactions are an important strategy in reaction design, allowing streamlining of chemical synthesis. Here we report a cascade Suzuki–Miyaura/Diels–Alder reaction, employing vinyl Bpin as a bifunctional reagent in two distinct roles: as an organoboron nucleophile for cross-coupling and as a Diels–Alder dienophile. Merging these two reactionsenables a rapid and operationally simple synthesis
Enynes, easily obtained by the Sonogashira coupling reactions of aromatic iodides. undergo. with good yields, en ne metathesis using the Grubbs catalyst. The resulting dienes are interesting carbo- and heterocycles which can give complex natural frameworks by Diels Alder reactions. Thus. an estradiol type skeleton is obtained in two steps from the corresponding enynes. An example of a metathesis-Diels-Alder cascade one-pot process is reported. (C) 2001 Elsevier Science Ltd. All rights reserved.
QUIN, L. D.;GORDON, M. D.;MACDIARMID, J. E., J. HETEROCYCL. CHEM., 1982, 19, N 5, 1041-1044