PALLADIUM-CATALYZED ADDITION OF ALKYNE TO NORBORNENE DERIVATIVES - UNUSUAL RING FORMATION AND EXPANSION REACTIONS

Treatment of norbornadiene (NBD) with BrCCPh and HCCPh in the presence of Pd(PPh3)4 and triethylamine gave the multiple-ring product 5a, which is constructed from two NBD and two PhCC groups. Norbornene (NBE) reacts similarly with BrCCPh and HCCPh and with BrCCCH2OCH3 and HCCCH2OCH3 to afford 5b,c, respectively. The structure of 5b was determined by X-ray diffraction. Crystal data for 5b: orthorhombic, Pbca, a = 11.329(7) angstrom, b = 16.218(12) angstrom, c = 24.297(8) angstrom, Z = 8. In the presence of formic acid and triethylamine, the reaction of 1-bromoalkyne with NBD or its derivative catalyzed by Pd(PPh3)4 afforded product 6 (NBD and BrCCPh, 6a; NBE and BrCCPh, 6b; NBE and BrCCCH2OCH3, 6c). The skeleton of 6 is the same as that of 5 except that the alkynyl substituent in 5 is replaced by a hydrogen atom in 6. The reaction of 1,4-epoxy-1,4-dihydronaphthalene (EHN) and 5,8-(CH3O)2EHN with HCCPh under conditions similar to those for 5a afforded 8a and 8b, respectively. Treatment of EHN, 5,8-(CH3O)2EHN, and exo-dimethyl-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate with BrCCPh under conditions similar to those for 6a gave products 9a-c, respectively. Both 8 and 9 contain two EHN and an alkyne molecule. The structure of 8b was also determined by X-ray diffraction. Crystal data for this compound: triclinic, P1BAR, C32O6H30, a = 9.2000(23) angstrom, b = 9.912(4) angstrom, c = 15.164(6) angstrom, alpha = 83.73(3)-degrees, beta = 76.60(3)-degrees, gamma = 77.00(3)-degrees, Z = 2. Mechanisms involving multiple insertions are proposed to account for the formation of 5-9 and the stereochemistry of these compounds.