Cyclopropane ring systems

The construction of cyclopropane ring systems is of great interest for organic chemists due to the existence of such rings as a basic tmit in a number of natmal products and several active drug substances. Numerous accounts of the synthetic methods used to construct this unique structural unit have been reported.  

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An intriguing reaction has been reported that does not exactly fit into the category of Michaelis-Arbuzov reaction but does involve nucleophilic attack of a neutral trivalent phosphorus for generation of a new C-P bond. Phenyl- and methyldichlorophosphine have been reported to attack the strained cyclopropane ring system of 1,3-dehy-droadamantane, overall adding P-Cl across the most strained bond of the ring system (Equation 3.5).140... 

A most convenient method for the formation of cyclopropane ring systems is the... 

Incorporation of the choline portion of acetylcholine (37) into a cyclopropane ring system resulted in cis- and rans-l,2-disubsti-tuted molecules, (38)and (39), in which the... 

The formation of cyclopropanes by the addition of carbenes to alkenes was first reported by Doering and Hoffmann in 1954/ Since then, this most characteristic reaction of carbenes has been successfully exploited for the synthesis of cyclopropanes. The cyclopropane ring system is not only found as a structural element in a wide range of natural products, but is also a very useful synthetic intermediate leading to a variety of cyclic and acyclic compounds. ... 

Yatakemycin, an exceptionally potent, naturally occurring antitumor agent isolated from a culture broth of Streptomyces sp. TP-A0356 in 2003. (-l-)-Yatakemycin contains a characteristic dienone cyclopropane ring system which also occurs in other antitumor compounds that possess remarkable antitumor activity via a sequence-selective DNA alkylation at the activated cyclopropane [Y. Igarashi et al., J. Antibiot. (Tokyo) 2003, 56, 107 M. S. Tichenor et al., J. Am. Chem. Soc. 2004, 126, 8396 ... 

The sp carbon nuclei of the cyclopropane ring system appeared at 8 72. 

A range of novel compounds possessing structures incorporating a polyfluoro-cyclopropane ring system has been synthesized during work on the new and extremely toxic gas perfluoro(methylenecyclopropane) (see p. 59). ... 

This method runs into difficulties with highly branched or strained bond connectivities because several spherical caps may overlap and the cap volumes may be subtracted more than once. For example, the volume is underestimated by some 10% for cyclopropane ring systems. Alternatively, Vm can be calculated more accurately [10] by subdividing a parallelepiped box that contains the whole molecule into a very large number of small cubes, and counting the number of those elementary cubes that are inside at least one atomic sphere (Ain). If V° is the volume of the cube (typically, 10 A ), one gets... 

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