Cyclopropyl—cyclobutyl

Die Autoren schlieBen aus ihren Ergebnissen auf einen allgemeinen elektronenanziehenden Effekt der Cycloalkylgruppen, welcher in fol-gender Weise von der RinggroBe abhangig ist Cyclopropyl>Cyclobutyl... 

Reactions of Cyclopropyl, Cyclobutyl, Cyclopentyl and Cyclohexyl-p-Toluenesulfonates and Halides. J. Amer. chem. Soc. 73, 5034 (1951). 

Of special interest is the use of protected cyanohydrins in the formation of carbocyclic rings. Ring closure of an acyclic intermediate to form a five-membered ring (75-85%) has been Ascribed in the synthesis of prostaglandins (equation 17). In addition this method is applicable to the formation of cyclopropyl, cyclobutyl and cyclohexyl rings (60-70%). ... 

The cationic ring enlargement of cyclopropylmethyl derivatives to cyclobutanes is a well-known reaction which has been extensively studied in order to illuminate the true nature of the intermediate cyclopropylmethyl/cyclobutyl cation (see also Sections 2.1 and 5.1). In many of the cases reported mixtures of cyclopropyl, cyclobutyl or homoallyl compounds are obtained which, although interesting for mechanistic and theoretical studies, are not of much synthetic value. Therefore, in this section, cyclopropane to cyclobutane ring enlargements involving cyclopropylmethyl derivatives will be restricted to synthetically useful cases. 

The compounds in this section, listed in Table 29, comprise cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups and their ring-substituted derivatives (Nos. 1 to 32) and a few compounds with polycyclic ligands (Nos. 33 to 40). 

Theoretical calculations indicate ttiat the barriers for 1,2-hydride shifts in carbocations are ordered as follows cyclopropyl > cyclobutyl > cyclopentyl > sec-butyl. Propose an explanation for this trend. 

Efforts to produce the cyclopropylamino-radical for e.s.r. studies gave only ring-opened imine radicals. Ring-openings of cyclopropyl, cyclobutyl, and bicyclo[n,l,0]alkyl radicals have been reported and the disrotatory nature of the ring-opening of cyclopropyl radicals has been established by examination of ring-fused systems. ... 

A possibly useful synthesis of substituted cycloheptenes has been developed which involves pyrolysis of cyclopropyl-cyclobutyl systems, e.g. (127) gave (128). ... 

Different cyclopropyl-, cyclobutyl-, cyclopentyl-, cyclohexyl-, cycloheptyl- (or higher) carbenes are known. A survey is provided in the literature. In general, the shift of an alkyl group results in ring... 

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