Cycloadditions small ring compounds

The two articles in this current volume describe recent developments with small ring compounds which have not teen compiled in such a context before. T. Hirao discusses selective transformations initiated by transition derivatives in the construction of functionally substituted five-, six- and seven-membered rings as well as open-chair compounds. Cycloadditions onto methylene- and alkylidene-cyclopropane derivatives, described by A. Goti, F. M. Cordero and A. Brandi, not only yield products with spirocyclopropane moieties which can be desirable as such or as potential mimics of gem-dimethyl groupings, but also intermediates which can undergo further transformations with ring-opening of the cyclopropane units. 

Cyclopropanones act as three-carbon sources in [4 + 3] cycloadditions. However, these small-ring compounds are impractical for preparative scale experiments, because they are generally inaccessible and also must be handled with special precautions, in contrast to other oxyallyl species. One of the early descriptions of the synthesis of cyclopropanones appeared in 1932. NeverAeless, the development of the chemistry of cyclopropanones proceeded at quite a slow pace until the late 1960s when Turro reported their utilization in [4 -i- 3] cycloaddition reactions. 2,2-Dimethylcyclopropanone (14) adds to furan, cyclopentadiene, 6,6-dimethylfulvene and the relatively nucleophilic N-methylpyrrole to give the corresponding cycloproducts, but fails to react with anthracene and 1,3-butadiene. Parent cyclopropan-one cannot be used. 

Metal-catalyzed Cycloaddition of Small Ring Compounds... 

Highly strained carbon-carbon double bonds and even carbon-carbon o-bonds of small ring compounds interact readily with transition metal complexes. Such perturbation activates them to enter into intra- and inter-molecular cycloadditions with cleavage of caibon-[Pg.1185]

Ohta T, Takaya H (1991) Metal-catalyzed cycloaddition of small ring compounds. In Trost BM, Fleming I (eds) Comprehensive organic synthesis, vol 5. Pergamon, Oxford, p 1185... 

For a review on Cycloadditions onto Methylene and Alkylidenecylopropane Derivatives see Goti, A. Cordero, F.M. Brandi, A. in Small Ring Compounds in Organic Synthesis V, A. de Meijere, Ed., Topics Curr. Chem., Springer Berlin, Heidelberg 19%, p2ff. 

Metal-Catalyzed Cycloaddition of Small Ring Compounds. T. Ohta and H. Takaya, Comp. Org. Synth., 1991, 5, 1185-1205. 

There are so many different examples of photochemical dimerizations and cross-cycloadditions 8-11,13-17) 0f olefinic compounds that one is not surprised to find several variations of mechanistic patterns. Simple olefins, including dienes and strained small ring, bicyclic olefins and styrene derivatives form a class of compounds that undergo such reactions sensitized by triplet energy donors. Some examples axe given in Eqs. 19—23, where only cyclobutane products are depicted. Theory... 

Keywords Absolute configuration. Amino acids, Bicyclopropylidene, Coupling reactions. Cycloadditions, Cyclopropanation, Cyclopropanes, Organolithium derivatives. Palladium catalysis. Radical reactions. Small ring polycycles, Spiro compounds. Strain energy. Sulfides... 

Only a few papers on the formation of compounds with small rings have been published. One example is the [2 + 2]-cycloaddition of electron-rich enamines to Schiff bases under high pressure (1.4 GPa) (87JOC365). The reaction leads to substituted azetidines (1). Four-membered ring heterocycles, thietane derivatives (4), are formed by interaction of sulfene (2) with enamines (3) (86CB257 93JOC3429). 

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