Methylenecyclobutane, ring strain

Due to the ring strain in the cyclobutane ring, /(-carbonyl cyclobutanones made by oxidation of methylenecyclobutane in methanol will readily undergo retro-Claisen-type reactions. For ozonolysis, this can be avoided by changing the solvent from methanol to dichloromethane treatment of 6-methyl-8-methylene-m-3-oxabicyclo[4.2.0]octan-2-one with ozone in methanol gave methyl 2-(4-methyl-2-oxo-4-tetrahydropyranyl)acetate (1), while the same treatment in dichloromethane gave 6-methyl-m-3-oxabicyclo[4.2.0]octane-2,8-dione (2).16... 

A further addition of diazomethane to the strained exocyclic double bond of methylenecyclopropane gave a mixture of 4,5-dihydro-37/-pyrazoles. Separation of the 4-spiro-sub-stituted isomer by preparative GC and pyrolysis gave spiropentane 56.Note the formation of the methylenecyclobutane. In this case, the alkene-forming side reaction is in part driven by the relief of ring strain. Alternatively, spiropentane derivatives were obtained by treating an allene with an excess of diazoalkane and deazetization of the bisadducts 57 formed, e.g. formation of 1,1,4,4-tetramethylspiropentane (58). ... 

Exocyclic unsaturation can stabilize small ring heterocycles. In three-membered rings it is difficult to separate the contributions from increased angle strain and from electronic interactions between the unsaturation and the heteroatom. In four-membered rings such separation has been done (74PMH(6)199, p. 235). The CRSEs change "from oxetane (106 kJ mol-1) by -11 kJ mol-1 to oxelan-2-one (95 kJ mol-1) (corrected for electronic effects) and 4-methyleneoxetan-2-one (95 kJ mol" ). In contrast, an increase of 10 kJ mol 1 over the value for cyclobutane (111 kJ mol-1) is observed on going to both methylenecyclobutane and l,3-bis(methylene)cyclobutane. 

A series of lanthanide metallocene catalysts are active in the regioselective ring-opening polymerization of strained f .vo-rnethylcnecycloalkanes to yield f . v>-mcthylene-functionalizcd polyethylenes.9 a Methylenecyclobutane affords the polymer [-CH2CH2C112C( =CH2)-] under the catalytic action of [ 1,2-... 

The thermal decompositions of several types of strained hydrocarbons produce diradicals containing the cyclopropylmethyl unit. 1,3-Diradicals of type 2 are formed on thermolysis of spiropentane (1) in the gas phase, in a sealed tube, or in a flow system. Diradical 2 not only ring closes back to spiropentane, but also rearranges by -scission to produce the new delocalized diradical 3, ring closure of which generates methylenecyclobutane 4) A competing reaction which yields allene and ethene is minor, provided the pyrolysis temperature is not allowed to rise higher than ca. 400 °C. 

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