Geminal cyclopropane rings

This survey will be closed by structures of the type 13, where two pairs of geminal bonds of the cyclopropane ring are joined by a four-dentate substituent. Bridged propellanes (Section VII.C.2) are also members of this class. 

In cyclopropane rings three types of coupling constant are possible (1) vicinal (cis), (2) vicinal (trans) and (3) geminal. The geometry of the cyclopropane ring indicates that the dihedral angle between cis-vicinal protons is 0° whereas that between trans-vicinal... 

A cyclopropane ring fused to a further ring as in 245 has proved to be a particularly apposite substrate for the detection of the so-called halolithiocarbenoids such as 246 (this compound is formed from the geminal dibromide with n-butyl lithium). At — 100°C in... 

Notably, the two geminal substituents on the cyclopropane ring stabilize both the norcaradiene and the bicyclo[2.1.0]pentane ( housane ) structure with respect to valence isomerization. The 3,3-dimethyl-3i/-pyrazoles mentioned above are prepared readily by 1,3-dipolar cycloaddition of 2-diazopropane to cyanoacetylenes. A more convenient synthesis of 4,5-dicyano-3,3-dimethyl-3//-pyrazole is the [3-1-2] cycloaddition of 2-diazopropane to fumarodinitrile, followed by oxidation of the 5,5-dimethyl-2-pyrazoline thus obtained with manganese dioxide. 

In the dehydrobromination of 9-bromobicyclo[6.1.0]nonane (37), which has no alkyl group geminal to the bromine, the initial product is a cyclopropene intermediate in which the double bond undergoes rapid base-catalyzed migration to a position exo to the cyclopropane ring. An 80% yield of product was thereby obtained in which the major component (95%) was bicyclo[6.1.0]non-l -ene (38). ... 

Chlorocyclopropyl sulfides 71 are easily methanolyzed at ambient temperature into the corresponding 5,0-acetals of cyclopropanone. The methanolysis is accelerated by the introduction of methyl groups on the cyclopropane ring, with each geminal dimethyl pair increasing the rate by approximately fourfold. ... 

It soon became evident that the ester structure is necessary for their activity and both the acidic and the alcoholic hydrolysis products are inactive. Also the geminal methyl groups on the cyclopropane ring and the unsaturated side chains proved to favour insecticidal action. Based on these considerations Schechter et al. (1949) synthesised the ( )-3-allyl-2-methyl-4-oxo-cyclopent-2-en-l-yl ester of ( )-( ,. chrysanthemic iund (27) which became known under the name allethrin. 

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