Cyclopropanes and alkenes

Methoxycarbonyl and acetyl derivatives Relative rates of decomposition into cyclopropanes and alkenes 75JCS(P2)1791... 

These observations indicate that there is no sharp borderline between cyclopro-panating and metathesis-catalyzing carbene complexes. Fortunately the number of carbene complexes which mediate both cyclopropanation and alkene metathesis is rather small, and in the detailed overview given in the following sections it will become apparent that most carbene complexes are highly selective and thus valuable reagents for organic synthesis. 

Nickon and Westeriuk (1967) have given an interesting analysis of 1,3-eliminations and cyclopropane ring cleavages. (These are also examples of the similarity in cyclopropanes and alkenes, with respect to... 

To a synthetic chemist the analogy between cyclopropanes and alkenes is indeed an appropriate one. Virtually every reaction that an alkene undergoes has its counterpart in the repertoire of transformations possible with cyclopropanes. Thus conjugation of a cyclopropane to an alkene makes it possible to invoke a number of reaction modes and reactive intermediates that can be compared directly to their alkenic counterparts. 

Thermal deazetization of pyrazolines results in the formation of cyclopropanes and alkenes, illustrated in Figure 44 for the parent compound (18). This reaction is of interest in that one could imagine that it would involve the same trimethylene biradical (19) proposed to be an intermediate in cyclopropane stereomutation (Section III.A). Supporting this notion is the observation that the parent pyrazoline gives 89% cyclopropane and 11 % propylene at 250° C. If one took this product ratio as a reflection of the branching ratio from a common trimethylene intermediate, it should then be possible to compare these figures with the relative rates of stereomutation and propylene formation from cyclopropane-d2 . Interestingly, they are identical. 

Benzyl esters and carbamates in the presence of other easily reducible groups such as aryl bromides, cyclopropanes, and alkenes are selectively cleaved with tri-ethylsilane and palladium chloride. ... 

The cationic rearrangement of cyclobutyl compounds to cyclopropylmethyl derivatives is a well-studied reaction which, like the homoallylic rearrangement, has been mainly investigated in connection with the fate and nature of the cyclobutyl cation.Again the synthetic value of this rearrangement is limited because generally mixtures of cyclobutanes, cyclopropanes and alkenes are obtained. 

The photodecompositions of 3,3-bis(l,l-difluorohexyl)diazirine and 3-(l,l-difluoro-octyl)-3//-diazirine have been examined. On irradiation in cyclohexane or methanol, competing photoisomerization to linear diazo-compounds and photofragmentation via carbene intermediates to cyclopropanes and alkenes has been observed and is illustrated for 3,3-bis(l,l-difluorohexyl)diazirine (6) in Scheme 1. The majority of investigations of nitrogen photoelimination in cyclic... 

The difference between cyclopropane and alkenes on the one hand and alkanes on the other is nowhere more clearly seen than in the kinetics of their reactions with hydrogen and in the relative activities of metals for those reactions. The ranking of metals activities for cyclopropane hydrogenation, namely,... 

Two reviews address the reactions of bare transition metal atoms and ions with hydrocarbons in the gas phase and the reactions of monosubstituted alkanes with bare transition metal ions. 2 A study of the reactivity of ground-state, neutral transition metal atoms from the left hand side of the 4d series (Y through Mo) shows that they are unreactive towards linear alkanes but that they will react with cyclopropane and alkenes.3 Atomic metal cations form a 1 1 adduct with tribenzocyclotriyne in a Fourier-transform ion cyclotron resonance spectrometer. Reaction of molecular oxygen with M(C2H4) results in ligand exchange to M02 for the early first row transition metals. Activation of the O—O bond and product formation is observed for ccnnplexes of Sc+,Ti+andV+.5... 

Fragmentation Generally, spectra of cyclopropanes and alkenes are very similar because at 70 eV ionization, the ring readily isomerizes to corresponding alkene radical cations. 

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