848927-36-6Relevant articles and documents
Facile construction of spirocyclopropanated bi-, tri- and tetracyclic skeletons by novel cascades involving intra- and intermolecular heck reactions of 2-bromo-1,6-enynes and bicyclopropylidene
Schelper, Michael,De Meijere, Armin
, p. 582 - 592 (2005)
Acyclic 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-1,4′-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 the tetraenes and bicyclo[4.3.0]nonadiene and its heteroanalogues were obtained with bulky substituents at the alkyne terminus of the precursors. Heteroatom-containing precursors 9-R and H-R gave lower yields than their all-carbon analogues 5-R. The acyclic 2-bromo-1,8-dien-6-ynes 28a,b,c upon palladium-catalyzed co-cyclization with bicyclopropylidene (12) at 110 °C gave spirocyclopropanated tricycles 31a,b and 32, respectively, in moderate yields (14, 31 and 32%). These products were formed by two consecutive 6π-electrocyclizations. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
