Spirocyclopropane ring

Since it is well known that cyclopropane rings are better electron donors than dimethylmethylene groups, especially towards electron-deficient or electron-attracting centers [9,10], in macrocycles such as 48 it would be expected that the spirocyclopropane rings rather than the dimethylmethylene groups in [nlpericyclines would more efficiently transmit the electronic interaction between the triple bonds (Fig. 2). 

A new selective thermal cascade ring-enlargement process of 4-chloro-substituted spiro[cyclopropane-l,5 -isoxazolidines], leading to a new method for the synthesis of the indolizine skeleton, has been reported (see Scheme 17). Apparently, the process is made possible by the presence of a chlorine substituent on the carbon a to the spirocyclopropane ring which facilitates a cyclopropyl-to-cyclobutyl ring enlargement mediated by a polar solvent. 

CC 1065 108 is a highly toxic antibiotic isolated from Streptomyces zelensis containing a reactive spirocyclopropane ring. It cleaves DNA through a mechanism similar to the cleavage which occurs upon treatment of DNA with the carcinogenic ptaquiloside 25 (vide supra. Sect. 2.6), namely by depurination of alkyladenine adducts, Eq. (43) [142]. 

Thiony I chloride dimethy Iformamide Spirocyclopropane ring gem-Dimethyl effect on ring closure... 

Catalyst -, Geo -, Metal -, Nucleophile -, Regio-, Stereo-, Wavelength -iryn-an z-Specificity -, isoxazolidine ring from nitrones 16, 735s31 Spirocyclopropane ring opening, double, paracyclophanes by -30, 472... 

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