Palladium-catalyzed cross-coupling reaction of 1,1-diboryl-1-alkenes with aryl and alkenyl iodides was found to proceed stereoselectively, giving rise to the corresponding mono-coupled product as a single diastereomer with E-configuration. Second coupling of the initial product with another aryl iodide affords diverse triarylalkenes in their stereochemically pure form. This highly stereoselective approach for triarylalkenes allows one to synthesize both diastereomers in one pot from 1,1-diboryl-1-alkenes.

Keywords: Cyclopropane / Palladium / Transition metal / Cascade reactions / ElectrocyclizationAcyclic 2-bromo-1,6-enynes 5-R, 9-R and 11-R with bulky substituents at the acetylenic terminus were co-cyclized with the highly strained bicyclopropylidene (12) under palladium catalysis at 80°C to give the cross-conjugated tetraenes 13-R, 18-R and 19-R in moderate-to-good yields (34−71%). Only the co-cyclization of 5-Ph gave rise to an additional product, which was identified as the 11-membered ring 20. At elevated temperatures (120−140°C) the initially formed tetraenes underwent 6π-electrocyclization to give spiro [cyclopropane-1,4Ј-bicylo[4.3.0]-1(6),2-dienes] 21-R, 22-R and 23-R. This novel class of spirocyclopropanated oligocycles is also accessible by a one-pot protocol. The highest yields for both

Cyclopropylidene lithium carbenoids reacted with bis(pinacolato)diboron in THF/Et2O at −110 °C to give various 1,1-diborylated cyclopropanes in good yields. Treatment of the diborylated cyclopropanes with 3-chloro-1-lithio-3-methyl-1-butyne produced the corresponding diborylated allenylcyclopropanes, which underwent ring-expansion in the presence of a Rh catalyst to give 1,2-diborylated methylenecyclopentenes conveniently.

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