Stereoselective Cyclopropanation of 1,1-Diborylalkenes via Palladium-Catalyzed (Trimethylsilyl)diazomethane Insertion
Oriol Salvado1, Paula Dominguez-Molano1, Elena Fernández1
1Departament de Química Física i Inorgànica, University Rovira i Virgili, 43007 Tarragona, Spain.
Abstract:
Palladium catalyzes the cyclopropanation of 2-substituted 1,1-diborylalkenes with (trimethylsilyl)diazomethane. The relative stereoselectivity is controlled via a carbene insertion sequence generating an exclusive anti conformation between the R and SiMe3 substituents. Mixed 1,1-diborylalkenes also contributed to the formation of stereoselective B, B, Si-cyclopropanes. Orthogonal activation with NaOBu gives protodeborylation preferentially on the boron moiety syn to the aryl group. Further oxidation gives access to polyfunctional cyclopropyl alcohols with controlled enantioselectivity when chiral boryl motifs are involved.
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