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Reaction of 1,1-dichloro-2,5-diphenylcyclopropabenzene 6 with Meldrum's acid 8 in the presence of pyridine leads to coupling of the cycloproparenyl cation 7 with the stabilized diketo anion 9. Subsequent, spontaneous, base-induced dehydrochlorination gives the alkylidenecyclopropabenzene 11 in a one-pot reaction. Flash vacuum thermolysis of 11 at 650 °C ejects acetone and carbon dioxide, giving cyclopropabenzenylidenethenone 12 that is isolated in an Ar matrix at 20 K and characterized by a strong ketene band at 2107 cm-1 in the IR spectrum.

Electrochemical and modulated specular reflectance spectroelectrochemical (MSRS) investigations were performed on 1- (diphenylmethylene)cyclopropabenzene in nominally dry acetonitrile solution. The results indicate the formation of a stable anion radical and a quasi stable cation radical. The first order homogeneous rate constant for the decay of the cation radical was computed. Cycloproparenes possess some of the highest strain energies known; the parent compound I has a strain energy of 68 kcal/mol. As a result, the electrochemical oxidation and reduction potentials of the neutral molecules are lower than those of most other electroactive hydrocarbons.

The Helium (I) photoelectron spectra of benzo and naptho derivatives of 1,1-diphenylmethylenecyclopropene (DPMC) are presented. A correlation of electro-chemical oxidation potentials E sub 1/2 (+) values and gas phase ionization potentials of a series of aromatic hydrocarbons is discussed. This correlation suggests that the difference in E sub 1/2 (+) values for the two DPMC derivatives is due to structure specific solvation of the radical cations . H/3 and HAM/3/CI calculations are compared with a simple structure derived analysis of the observed pe spectra. It is suggested that the effects of the fused cyclopropene grouping are to be found in small reductions of the second or higher ionization energies.

The present study has been directed towards the synthesis and base promoted rearrangements of some saturated and unsaturated halogenotricyclo-octanes. The preparation of a number of previously unknown 4,4,8- and 4,4,8,8-tetra-halogeno-anti-tricyclo[5,1,0,03,5]- octanes and the corresponding 3,3,8-tri- and 3,3,8,8-tetra-halogeno-anti-tricyclo[5,1,0,02,4] octanes has been accomplished and the stereo-chemistries of their ring systems established. The former tricyclo-octanes are base sensitive and on treatment with potassium t-butoxide give rise to mixtures of (E) - and (Z) -Beta-t-butoxystyrenes. However, the anti-tricyclo[5,1,0,02,4] octanes give no characterisable products on treatment with base. The mechanistic implications of the tricycle-octane - styrene conversion have been studied in some detail and halogenocyclo-octatetraenes and phenylacetylenes have been eliminated as intermediates. The behaviour of several methoxy-substituted 4,4,8,8-tetrahalogeno-anti-tricyclo[5,1,0,03,5] octanes with the same base has been studied, and it has been found that homotropilidenes are formed regiospecifically by 1,4-elimination. These conversions constitute the first known examples of such elimination experienced by ring-fused halogenocyclopropanes. From these studies, evidence is presented which implicates homotropilidenes and bicyclo[4,2,0]octa-2,4-dienes as intermediates in the production of styrenes, and a mechanism for the tricyclo-octane - styrene rearrangement has been proposed. A new and potentially versatile synthesis of 3,3-dihalogeno-anti tricyclo[5,1,0,02,4] oct-5-enes (anti-bishomobenzenes) has been developed. The new route employs readily available starting materials, involves sequential introduction of the cyclopropyl, gem-dihalogenocyclopropyl, and olefinic moieties and proceeds in an overall yield of about 14%. This represents a five-fold increase over the previously reported yields.

The aim of the present study has been the synthesis of 1H-cyclo-Propa[1]phenanthrene (16a) and its derivatives, the sole remaining unknown structural type of the cycloproparenes. Established procedures for cycloproparene synthesis are not readily adaptable to this ring system, and routes based upon new bridge-head-substituted 1a,9b-dihydrocyclopropa[1]phenanthrenes are examined. 1, 1-Dichloro-1a-phenylseleno-1a, 9b-dihydrocyclopropa [1] phenanthrene (73) is prepared by the addition of dichlorocarbene to the corresponding phenanthrenyl selenide (72). syn-Selenoxide elimination of PhSeOH from the derived selenoxide (74) gives 1,1-dichloro-1H-cyclopropa[1]phenanthrene (76) which is intercepted by methanolysis. Labelling studies provide convincing evidence for the intermediacy of the 1H-cycloproparene. The viability of an oxidative decarboxylation route to 1,1-dialkyl-1H-cyclopropa[1]phenanthrenes is investigated for the model compound 7,7-dimethylbicyclo[4.1.0]hept-3-ene-1-carboxylic acid (122). A product of formal cyclopropyl-allyl cation rearrangement, is isolated. 1a-Methylseleno-1a,9b-dihydrocyclopropa[1]phenanthrenes (174) is prepared by the unprecedented addition of methylselenide anion to 1aH-cyclopropa[1]phenanthrene (63) (generated by a new route involving the fluoride ion-promoted elimination of the elements of chlorotrimethylsilane from the isomeric 1-chloro-1a-trimethylsilyl-1a, 9b-dihydrocyclopropa[1]phenanthrenes (170) and (171)). Treatment of the drived dimethylselenonium tetra-fluoroborate (179) with base in the presence of furan gives the endo- and exo-furan cycloadducts (180) and (181) of 1H-cyclopropa[1]phenanthrene (16a). The results presented herein provide the first conclusive evidence for the existence of the 1H-cyclopropa[1]phenanthrene ring system, both as the parent hydrocarbon (16a) and the 1,1-dichloro-derivative(76).