THE USE OF SUPPORTED REAGENTS IN THE SYNTHESIS OF REACTIVE INTERMEDIATES (METHYLENECYCLOPROPENE, CYCLOPROPENES)
Doctor of Philosophy
The first isolable hydrocarbon derivative of methylenecyclo- propene, 1,4-di-tert-butylmethylenecyclopropene, was synthesized. The chemical shifts of the olefinic protons revealed that the dipolar structure Ia makes a sizeable contribution to the resonance hybrid. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) Methylenecyclopropene was generated in vacuo in approximately 10% yield by dehydrochlorination of 2-chloromethylenecyclopropane using potassium tert-butoxide in tetrahydrofuran at -40(DEGREES)C and 0.5 torr. Nearly pure methylenecyclopropene could be prepared from the same precursor using a vertical column containing potassium tert-butoxide supported on Chromosorb W at 240(DEGREES)C and 10 mtorr. The nuclear magnetic resonance spectra (('1)H and ('13)C) were obtained at -100(DEGREES)C in tetrahydrofuran-d(,8). The exocyclic protons appear at (delta) 3.47 and the ring protons at (delta) 8.61. The exocyclic carbon resonates at (delta) 59.57 and the ring carbons at (delta) 132.90. The infrared spectrum was recorded at 15 K in an argon matrix. These chemical shifts and the presence of a strong transition in the infrared at 1770.3 cm('-1) show that IIa is an important contributor to the structure of methylene- cyclopropene. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) The vapor phase dehydrochlorination of either 1,4-dichlorospiro- pentane or 1-chloro-2-vinylcyclopropane over supported potassium tert-butoxide at 320(DEGREES)C and 10 mtorr yielded 1-vinylcyclopropene. Other supported reagents studied include methyllithium on glass helices and tetrabutylammonium fluoride on glass helices. These can be used to generate cyclopropenes from vicinal dihalocyclopropanes and (beta)-halosilanes, respectively. For example, 1-chlorocyclopropene, 1-chloro-2-trimethylsilylcyclopropene, 1-bromo-2-chlorocyclo- propene, bicyclo 4.1.0 hept-(1,7)-ene and bicyclo 4.1.0 hept- (1,6)-ene were synthesized by gas phase elimination reactions over these reagents.