Towards the synthesis of insulated oligoynes: a ring-closing-metathesis approach to molecular encapsulation

Masked hexayne 18 was prepared in I I steps from commercially available reagents. The four butenyl substituents contained within the two arylsilane residues in 18 have been used in a double ring-closing-metathesis operation in an attempt to encapsulate the pi-conjugated framework. When 18 was treated with Grubbs' 1st generation metathesis catalyst however, double ring-closing metathesis provided macrocycle 19 as the major product in good yield. Reasons why the macrocycle in 19 crowns, rather than encapsulates, the pi-conjugated framework are discussed. (c) 2006 Elsevier B.V. All rights reserved.