Ti-Catalyzed Barbier-Type Allylations and Related Reactions
作者:Rosa E. Estévez、José Justicia、Btissam Bazdi、Noelia Fuentes、Miguel Paradas、Duane Choquesillo-Lazarte、Juan M. García-Ruiz、Rafael Robles、Andreas Gansäuer、Juan M. Cuerva、J. Enrique Oltra
DOI:10.1002/chem.200802180
日期:2009.3.9
Versatility of titanium: Titanocene(III) complexes catalyze Barbier‐type allylations, intramolecular crotylations (cyclizations), and prenylations of a wide range of aldehydes and ketones. These reactions take place at RT under mild conditions compatible with many functional groups; provide good yields of open‐chain and cyclic homoallylic alcohols, including heterocyclic derivatives; and can be conducted
The first direct preparation of allylbarium reagents by reaction of insitu generated reactive barium with various allylic chlorides and their new and unexpected selective allylation reactions with carbonyl compounds are disclosed. Highly reactive barium was readily prepared by the reduction of barium iodide with 2 equiv of lithium biphenylide in dry THF at room temperature. A variety of carbonyl compounds reacted with barium reagents generated from (E)- or (Z)-allylic chlorides in THF at -78 degrees C. All reactions resulted in high yields with remarkable alpha-selectivities not only with aldehydes but also with ketones. The double bond geometry of the starting allylic chloride was completely retained in each case. Stereochemically homogeneous (E)- and (Z)beta,gamma-unsaturated carboxylic acids were easily prepared in good yields by highly alpha-selective carboxylation of allylic barium reagents with carbon dioxide. A selective Michael addition reaction with alpha,beta-unsaturated cycloalkanone was also achieved using an allylbarium reagent. Treatment of 2-cyclopentenone (1 equiv) with allylbarium chloride (2 equiv) in THF at -78 degrees C for 20 min afforded 3-allylcyclopentanone in 94% yield with a 1,4/1,2 ratio of >99/1. Furthermore, the in situ generated barium enolate was efficiently trapped with various kinds of electrophiles (Me(2)C=CHCH2Br, (C5H11CHO)-C-n, and CH3COCl).
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