Cooligomerizations of 3-Substituted 1,5-Hexadiynes with Bis(trimethylsilyl)acetylene Catalyzed by Cobalt. A General Synthesis of Tricyclic Ring Systems from Acyclic Precursors

A one-step synthesis of polycycles is described which utilizes a CpCo(CO)₂-catalyzed cooligomerization of substituted 1.5- hexadiynes with bis(trimethylsilyl)acetylene solvent to produce intermediate benzocyclobutenes which may be subsequently or concomitantly ring opened to furnish intermediate o-xylylenes. The latter dienes react intermolecularly with solvent to yield ultimately 2,3,6,7-tetrakis(trimethylsilyl)naphthalene (6), substrate to a variety of electrophiles. Intramolecular trapping by appended dienophiles results in the formation of tricyclic systems containing ortho-bis-silylated benzenes and a variety of heteroatoms via exo transition states leading to trans ring fused compounds. Only in one case, 31, was a significant proportion of the cis isomer observed. Protodesilylation may be achieved with acid to give the parent systems. In the case of 17 containing an aldehyde as a dienophile the cobalt-catalyzed cyclization results in ketal 22. A general synthetic entry into 3-alkylated 1.5- hexadiynes was found via the in situ generation of l,3,6-trilithio-l,5-hexadiyne.