Methylenecyclopentane ring

The annulation of a methylenecyclopentane ring has a peculiarity Lewis acids are ineffective as catalysts the reaction, however, takes place in the presence of fluoride42. 

Diethylaluminum hydride ethylene Methylenecyclopentane ring from 1,5-dienes... 

The TT-allylpalladium complexes 241 formed from the ally carbonates 240 bearing an anion-stabilizing EWG are converted into the Pd complexes of TMM (trimethylenemethane) as reactive, dipolar intermediates 242 by intramolecular deprotonation with the alkoxide anion, and undergo [3 + 2] cycloaddition to give five-membered ring compounds 244 by Michael addition to an electron-deficient double bond and subsequent intramolecular allylation of the generated carbanion 243. This cycloaddition proceeds under neutral conditions, yielding the functionalized methylenecyclopentanes 244[148], The syn-... 

The discovery of palladium trimethylenemethane (TMM) cycloadditions by Trost and Chan over two decades ago constitutes one of the significant advancements in ring-construction methodology [1]. In their seminal work it was shown that in the presence of a palladium(O) catalyst, 2-[(trimethylsilyl)methyl]-2-propen-l-yl acetate (1) generates a TMM-Pd intermediate (2) that serves as the all-carbon 1,3-di-pole. It was further demonstrated that (2) could be efficiently trapped by an electron-deficient olefin to give a methylenecyclopentane via a [3-1-2] cycloaddition (Eq. 1). 

Attempts to extend this reaction to the five-membered ring olefins 1-methylcyclopentene and norbomene resulted in 1-methylcyclopentane and methylenecyclopentane for the former and products (43)-(48) for the latter(80) ... 

Diisobutylaluminium hydride catalyses the ring-closure of various dienes. It is proposed that the process involves addition of the aluminium hydride to a terminal double bond, followed by ring-closure and, finally, elimination of the catalyst (equation 106). Thus 1,5-hexadiene gives methylenecyclopentane (213) (equation 107), 1,6-heptadiene gives methylenecyclohexane (214) (equation 108), 4-vinylcyclohexene gives bicyclo[3.2.1]oct-2-ene (215) (equation 109) and the spiro compound 217 is obtained from 5-methylene-l,8-nonadiene (216) (equation 110)112. 

The diester 226 undergoes ring-closure to the methylenecyclopentane derivative 227 in the presence of a catalytic amount of chlorotris(triphenylphosphine)rhodium in boiling chloroform saturated with hydrogen chloride. In contrast, if the reaction is catalysed by palladium(II) acetate, the isomeric cyclopentene 228 is produced (equation 115)118. 

Scheme 68 illustrates cyclopolymerization of 1,5-hexadiene catalyzed by a homogeneous chiral zirconocene complex to form optically active poly(methylenecyclopentane), whose chirality derives from configurational main-chain stereochemistry (757). This polymer is predominantly isotactic and contains predominantly trans cyclopentane rings. 

Fused methylenecyclopentanes of type 9 in which n = 3 or >6 when treated with KH and 18-crown-6 undergo a three-carbon ring expansion to give products of type 10 in about 90% yield. This ring expansion was used to convert the /f-keto sulfone (11)... 

Functionalized exo-methylenecyclopentanes can also be obtained by ruthenium-catalyzed intramolecular C-H bond activation [15]. l-(2-Pyridyl)-, l-(2-imidazolyl)-, and l-(2-oxazolyl)-l,5-dienes proceeded in a regiospecific manner to give five-membered ring products (Eq. 10). The proposed mechanism initially involves the activation of the vinylic C-H bond of the exocyclic C=C bond assisted by preliminary coordination of the nitrogen atom, followed by intramolecular insertion of the other C=C bond (see Eq. 6). 

Therefore, in the presence of phosphane-free or phosphane-modified Ni(0) catalysts, alkyl acrylates and alkyl crotonates codimerize with 2-methyl- and 2,2-dimethyl-methylenecyclopropanes to give Type B cycloadducts. The reactions turn out to be regio- but not stereoselective. The methyl group(s) bonded at the three-membered ring are always found at C-2 of the resulting methylenecyclopentanes, whereas the electron withdrawing group is bonded to C-4 (Eqs. 86 and 87) 27). 

As the proceeding chapters demonstrate, Ni(0)- and Pd(0)-catalyzed [3-1-21-cycloadditions of methylenecyclopropanes with alkenes open a new, simple, and useful route to a number of substituted methylenecyclopentanes. This catalytic generation of a trimethylenemethane synthon and its addition to olefinic double bonds not only lead to five-membered rings but also introduce an exocyclic methylene group, which is a useful functionality for further structural elaboration. 

The two Pd(0) or Ni(0) catalyzed [3+2]-cycloadditions starting with the readily accessible trimethylenemethane -precursors [2-(acetoxymethyl)-3-allyl]trimethyl-silan, methylenecyclopropane, and their substituted derivatives are important new methods for the synthesis of methylenecyclopentanes. Because of the simplicity with which many problems of cyclopentane-syntheses can be solved in a convenient one pot reaction this new methodology may be compared with the synthesis of six-membered rings by the powerful 4+2]-cycloaddition of the Diels-Alder reaction. 

Triorganylphosphane-modified palladium(O) compounds catalyze the codimerization of methylenecyclopropane with ethene, norbornene, dicyclopentadiene or norbomadiene to give substituted methylenecyclopentane derivatives. Here, in all cases, the three-membered ring is opened between C2 and C3. " ... 

---