A Formal [4 + 2] Dimerization of 9‐Cyclopropylidene‐9H‐fluorene

Abstract

The methylenecyclopropanes 7 and 8, with aryl substituents fixed in a coplanar conformation, show an extraordinary readiness to dimerize with formation of 10 and 11, respectively.

Three-Membered-Ring-Based Molecular Architectures

“…329 In spite of being a tetrasubstituted alkene, bicyclopropylidene (33) turned out to be a remarkably good ligand not only for cobalt but also for titanium, platinum, copper, and nickel. Thus, treatment of (Cp) 2 Ti(PMe 3 ) 2 (487) with 1.16 equiv of 33 in pentane gave (η 2 -bicyclopropylidene)(bis-η 5cyclopentadienyl)titanium(II) 488 in 79% yield as a green solid (Scheme 77). 329a Stable complexes of platinum(0) (489), 330 copper(I) (490), 331 and nickel(0) (491) 332 with a bicyclopropylidene ligand have also been obtained (Scheme 77).…”

Synthesis of Methylene- and Alkylidenecyclopropane Derivatives

“…284 The reaction of cyclopropylidenetriphenylphosphorane with fluorenone, surprisingly, did not provide the expected ACP 221, but the compound 222, a product of [4 + 2] cycloaddition between two molecules of 221, apparently unstable and very reactive in those conditions (Scheme 76). 285 On the other hand, an analogous ACP 223 obtained from indanone could be isolated and slowly underwent dimerization, however to the head-to-head [2 + 2] adduct 224 (Scheme 76). 285 Cyclopropanone, although spectroscopically detected at low temperature in inert solvents, 286 is not sufficiently stable to permit useful synthetic applications according to route B (Scheme 67).…”

“…285 On the other hand, an analogous ACP 223 obtained from indanone could be isolated and slowly underwent dimerization, however to the head-to-head [2 + 2] adduct 224 (Scheme 76). 285 Cyclopropanone, although spectroscopically detected at low temperature in inert solvents, 286 is not sufficiently stable to permit useful synthetic applications according to route B (Scheme 67). However, the hemiacetal 203 can provide a convenient source of the parent ketone.…”

“…The reaction of cyclopropylidenetriphenylphosphorane with fluorenone, surprisingly, did not provide the expected ACP 221 , but the compound 222 , a product of [4 + 2] cycloaddition between two molecules of 221 , apparently unstable and very reactive in those conditions (Scheme ) …”

“…On the other hand, an analogous ACP 223 obtained from indanone could be isolated and slowly underwent dimerization, however to the head-to-head [2 + 2] adduct 224 (Scheme ) …”