102. Solvolysen von 4-Alkylidenbicyclohept-2-en-6-olen. Synthese von 1-Vinylfulvenen und 8,8-Diphenylheptafulven

Article abstract of DOI:10.1002/hlca.19850680415

Solvolysis of 4-Alkylidenbicyclo<3.2.0>hept-2-en-6-oles.Synthesis of 1 Vinylfulvenes and 8,8-Diphenylheptafulvene.Four 4-alkylidenebicyclo<3.2.0>hept-2-en-6-ones 2-5, obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the 'endo'-alcohols 'endo'-6 to 'endo'-9 (68-73 percent) and 'exo'-alcohols 'exo'-6 to 'exo'-9 (3-20 percent).Treatment of some of these alcohols with (CF3SO2)2O in CH2Cl2/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10-12 or 1-vinylfulvenes 13 and 14, a new class of reactive tetraenes: Both 'endo'-9 and 'exo'-9, having two methyl groups at C(7), were converted into the vinylfulvene 13 (ca. 80 percent).The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as 'endo'-6 to 'endo'-8 afforded only the corresponding 7-membered-ring pyridinium salts 10-12 (66-79 percent), while 'exo'-6 produced only the vinylfulvene 14 (77 percent).A stereoelectronic control argument explains the C(1),C(5)-bond cleavage with 'endo'-B and 'endo'-6-'endo'-8, as well as the C(1),C(7)-bond cleavage with 'exo'-B, 'exo'-6, and with both 'endo'- and 'exo'-9.Thermolysis (120 deg) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19, respectively (ca. 90 percent); similar conditions (145 deg) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60 percent).When the iodide 22 derived from the triflate 12 with NaI was heated in refluxing toluene, 8,8-diphenylheptafulvene (23, 86 percent) was obtained.