Synthesis and chemistry of strained ring compounds

Abstract

The gas phase elimination of trimethylsilyl fluoride from beta-halocyclopropylsilanes using solid n-Bu4N+F or CsF adsorbed on glass helices offers a superior route to highly strained alkenes. This approach has been used to synthesize 1-chloro-3-methylenecyclopropene, 1,4-dichlorospiropentadiene, 1,4-dichlorospiropentene, and oxaspiropentene from the appropriate precursors. In each instance the product could be isolated and characterized by low temperature nuclear magnetic resonance spectroscopy. Geometries were defined computationally. The corresponding Diels-Alder adducts of these species with cyclopentadiene or 1,3-butadiene were also obtained and characterized.* Thermolysis of spiro[2.4]hepta-1,4,6-triene at 60°C yields bicyclo[3.2.0]hepta-1,3,5-triene (Ea = 24.7 kcal/mole) which dimerizes in two different fashions forming cyclobutanes. 1,2-Dimethylspiro[2.4]hepta-1,4,6-triene and 1-propylspiro[2.4]hepta-1,4,6-triene also rearrange at 60°C, but at a faster rate, to yield cyclobutane dimers of the corresponding bicyclo[3.2.0]hepta-1,3,5-trienes.* The reactions of benzocyclopropene and cyclopropa[b]naphthalene with metal carbenes were investigated. The cycloproparenes react with Cl2 (Cy3P)2Ru=CH2 to form unstable 3-ruthenabenzocyclopentenes which decompose to give o-xylylenes. o-Xylylenes produced in this way can be trapped as Diels-Alder adducts by dimethyl acetylenedicarboxylate. In contrast, Cp2Ti=CH2 forms moderately stable 2- and 3-titanabenzocyclopentene complexes.* *Please refer to dissertation for diagrams