Titanium(III) and samarium(II) induced rearrangements of vinyl cyclobutene derivatives

The catalytic or stoichiometric interaction of nickel(I) complexes with vinyl cyclobutenes has been a topic of investigation by our group for many years. The analogous interactions of titanium, samarium, iron and copper are the topic of the research described in this dissertation. Titanium(III), samarium(II) and iron(II) were found to be effective agents in transforming vinyl cyclobutene to a six-member product. In addition to the rearrangement, the titanium(III) and samarium(II) caused aromatization of the six-member ring. The formation of the aromatic phthalates (1,2-, 1,3- and 1,4-isomers) came directly from vinyl cyclobutene starting material. Transformation of 1,2-cyclobutadiene to an aromatic did occur but no 1,3- or 1,4-isomers were formed. Iron(II) compounds mediated a rearrangement from a vinyl cyclobutene to a six-membered diene with the subsequent conjugation of the diene's double bonds. Iron(II) did not cause aromatization. A mechanism suggests that the attack of titanium(III) and samarium(II) compounds on the ring double bond of vinyl cyclobutene occurs at the distal end of the ring double bond rather than the end proximal to the vinyl attachment. Further, deuterium labeling studies suggest that a mechanistic common intermediate is most likely.; The use of activated zinc to dechlorinate the dichloro vinyl cyclobutant, instead of bistriphenylphosphine nickel butene, was most fortuitous. In addition, THF, the usual solvent of the reaction was not conducive to titanium(III) and samarium(II) reactions since the THF deactivated the metal complex. There seems to be no direct relationship between standard aqueous oxidation/reduction potentials of the active metals and the ability to mediate either rearrangement or aromatization of the target compounds.