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

• Published in: European journal of organic chemistry Vol. 2005; no. 3; pp. 582 - 592
• Main Authors: Schelper, Michael, de Meijere, Armin
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.02.2005; WILEY‐VCH Verlag
• Subjects: Cascade reactions; Cyclopropane; Electrocyclization; Palladium; Transition metal
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.200400668

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 11‐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)