Daniel Frank

Cyclopropyl building blocks in organic synthesis. Part 81: Striving for unusually strained oxiranes: epoxidation of spirocyclopropanated methylenecyclopropanes

1-Oxa[3]triangulane 13, the epoxide of methylenespiropentane, is thermally stable up to 300°C, but immediately rearranges to spiro[2.3]hexan-4-one (7) in the presence of lithium iodide at ambient temperature. The permethylated bicyclopropylidene 10 is simply less reactive than the parent bicyclopropylidene (6a) towards dimethyldioxirane, but yields the isolable epoxide 11 (94%) with mCPBA. In contrast, the partially or fully spirocyclopropanated bicyclopropylidenes 18, 20, and 22, upon treatment with mCPBA or dimethyldioxirane, did not furnish the corresponding epoxides, but underwent oxidation with rearrangement to the corresponding cyclobutanones 19, 21 and 23 in yields of 59, 100 and 97%, respectively.

Effect of methyl substituents on the geometry and packing of some triangulanes and methylenecyclopropanes

The crystal structures of four derivatives of triangulanes and methylenecyclopropanes have been determined. The effect of permethylation on the geometry of the triangulane skeletons has been discussed in terms of the general bond increment scheme. Molecules 1, 3 and 4 are packed according to the “key-lock” principle, while packing of molecules 2 is determined by C–H⋯C interactions.

CCDC 631611: Experimental Crystal Structure Determination

Related Article: A.de Meijere, S.Redlich, D.Frank, J.Magull, A.Hofmeister, H.Menzel, B.Konig, J.Svoboda|2007|Angew.Chem.,Int.Ed.|46|4574|doi:10.1002/anie.200605150