Subscribe to RSS
Catalytic Asymmetric Allylic Alkylation with Vinylaluminum ReagentsContributor(s):Mark Lautens, Valentina Aureggi
Boston College, Chestnut Hill, USA
High Site- and Enantioselective Cu-Catalyzed Allylic Alkylation Reactions with Easily Accessible Vinylaluminum Reagents
J. Am. Chem. Soc. 2008, 120: 446-447
21 February 2008 (online)
allylic alkylation - vinylaluminum - DIBAL-H
A new efficient method for catalytic asymmetric allylic alkylation of allylic phosphates with vinylaluminum reagents is reported. The desired products are obtained in good yields and with enantioselectivities up to 98% ee.
The vinylaluminum reagents are prepared and used in situ by reaction of commercially available DIBAL-H with terminal alkynes. The asymmetric allylic alkylations are promoted in the presence of a readily available chiral N-heterocyclic carbene complex and a commercially available and air-stable copper salt. The desired products are obtained in relative short time (2-12 h) in 74-95% isolated yields, 77% to >98% ee, and with >98% E-selectivities. Various allylic phosphates can be used, including trisubstituted and disubstituted olefines. Vinyl bromides and cyclic alkenes are also suitable substrates for the allylic alkylation. A variety of terminal alkynes can be employed, including conjugated enynes. The hydroalumination/catalytic AAA sequence can be performed in a single vessel, on gram scale.