Spirocyclopropanated bicyclopropylidenes: straightforward preparation, physical properties, and chemical transformations.
In: Chemistry--A European Journal, Jg. 7 (2001) ; Nr. 18, S. 4021-4034
Zeitschriftenaufsatz / Fach: Chemie
The prepn., crystal structures, phys. properties, and reactions of spirocyclopropanated bicyclopropylidenes such as I were studied. I was prepd. in three steps and 24% yield from 7-cyclopropylidenedispiro[188.8.131.52]heptane, or, more efficiently, in one step by a dehalogenative coupling of 7,7-dibromotriangulane II (82%). Reductive dimerization was also used successfully in the prepn. of (E)- and (Z)-bis(spiropentylidene) and even of the \"third-generation\" spirocyclopropanated bicyclopropylidene III (17% yield over three steps from II). Whereas the parent bicyclopropylidene dimerized at 180 DegC to yield rotane, dimerization of I at 130 DegC under 10 kbar pressure occurred only with opening of one three-membered ring to yield the polyspirocyclopropanated (cyclopropylidene)cyclopentane deriv. IV in 34% yield; at elevated temp., the polyspirocyclopropanated 2-cyclopropylidene[3.2.2]propellane deriv. V was isolated in 25% yield. I and III underwent addn. of bromine, hydrogen bromide, and various dihalocarbenes to the central double bond without rearrangement. A branched triangulane and a branched dichloro-C2v-triangulane were used to prep. perspirocyclopropanated rotane (D3h-triangulane) VI (in six steps and in 1.4% overall yield from I) and the C2v-triangulane VII (in two steps and in 41% overall yield from III). Catalytic hydrogenation of I yielded 7,7'-bis(dispiro[184.108.40.206]-heptyl) and, under more forcing conditions, 1,1'-bis(2,2,3,3-tetramethylcyclopropyl). The bromofluorocarbene adduct of III reacted with butyllithium to give an unexpected polyspirocyclopropanated cyclopropylidenebicyclohexane deriv. as the main product along with the expected \"third-generation\" perspirocyclopropanated dicyclopropylidenemethane. Mechanistic aspects of the prepn. and reactions of spirocyclopropanated bicyclopropylidenes are discussed. The structures were characterized by X-ray crystal structure anal.; structural and crystal packing features are presented.