Bicyclo hept-1 cyclobutane

Carbenes are known intermediates in the thermolytic or photolytic decomposition of the lithium or sodium salts of tosylhydrazones, which, for endocyclic carbenes, results in ring contraction when the elimination of / - or y-hydrogens is impeded. Simple cyclobutanes generally cannot be prepared by this route from monocyclic cyclopentanone tosylhydrazones. However, the lithium salt of bicyclo[2.2.1]heptan-7-one tosylhydrazone gave bicyclo[3.2.0]hept-l-ene (4) as the major product (74%) by vacuum pyrolysis at 185 JC/20 Torr, together with bicyclo[2.2.1]heptane (14%) and tricyclo[2.2.1.02,7]heptane (12%) in 80% overall yield.67... 

On ultraviolet irradiation of bicyclo[2.2.1]hept-5-en-2-one in diethyl ether for 1 hour, the rearrangement product bicyclo[3.2.0]hept-2-en-7-one (33) was formed in 90% yield.103 Other bicyclo[n.m.l]alkenones gave the rearranged cyclobutane products, albeit in lower... 

Several photochemically induced vinylcyclopropane to cyclopentene rearrangements of nor-carene derivatives to form bicyclo[3.2.0]heptenes can be understood as ring contractions of cyclohexenes to cyclobutanes. Upon direct irradiation of norcar-2-ene (bicyclo[4.1.0]hept-2-ene) at 214 nm (pentane solution), however, complex product mixtures were obtained containing only small amounts of bicyclo[3.2.0]hept-2-ene, while toluene sensitized photolysis in 50 millimolar solution in degassed pentane at 254 nm gave mainly the cyclobutane derivative 13 in addition to EjZ-isomeric hepla-l,3,6-trienes.72... 

Cyclobutan 1 -Carboxy-2,2-dimethyl-3-formyl- IV/lb, 201 Cyclobnten 4,4-Dimethoxy-l, 2-dimethyl-3-oxo- E17f, 775 (1,5-Cl2 - 6,7-R2 — 3-oxo — 2,4-dioxa-bicyclo[3.2.0]hept-6-en/NaOH) Cyclohexan... 

Bicyclo[2.2.1]hept-2-en 5-Nitro-5-propyl- V/lc, 1071 (Diels-Alder) X/l, 397f. (Diels-Alder) Cyclobutan 1 -Cyan-3,3-dimethyl-l-ethoxycarbonyl- E17e. 226 [TosO —C2 —en(CN)2 + BH Ethanol]... 

The base-catalysed ring contraction of substituted cyclobutanes continues to attract attention and has been used for the synthesis of bicyclo[n,l,0]alkyl derivatives (n = 3 or 4) of known configuration. However, when applied to chlorotrialkylcyclobutane-1,3-diones, cyclopropanone-2-carboxylates are not obtained instead, ring cleavage occurs to give y-chloro-P-keto-esters, perhaps because of the ring strain associated with cyclopropanone. The dione (31), a photoproduct from bicyclo[2,2,l]hept-5-ene-... 

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