Cyclopentene derivatives 3-methyl

The carbonylation of dehydrolinalyl methyl carbonate (35) at room temperature affords the cyclopentene derivative 37 formed by the ene reaction of... 

An interesting strategy for the diastereoselective synthesis of five-membered carbocycles was achieved by the reaction of alkenylcarbene complexes and lithium enolates derived from simple methyl ketones [79]. The use of more or less coordinating solvents (THF or Et20) or the presence of cosolvents such as PMDTA allows the selective synthesis of one or the other diastereoisomer of the final cyclopentene derivative (Scheme 32). 

Water-soluble mthenium vinyUdene and aUenylidene complexes were also synthetized in the reaction of [ RuCl2(TPPMS)2 2] and phenylacetylene or diphenylpropargyl alcohol [29]. The mononuclear Ru-vinylidene complex [RuCl2 C=C(H)Ph)(TPPMS)2] and the dinuclear Ru-aUylidene derivative [ RuCl(p,-Cl)(C=C=CPh2)(TPPMS)2 2] both catalyzed the cross-olefin metathesis of cyclopentene with methyl acrylate to give polyunsaturated esters under mild conditions (Scheme 7.10). 

The course of the reductive photocyclization of enamines by irradiation in the presence of sodium borohydride depends on the nature of substituents. Thus the AT-methyl-S-phenyl compound 46 yields a mixture of the pyrrolidinone 47, the piperidinone 48 and the tricyclic compound 49, whereas the dimethyl analogue 50 gives the piperidinone 51 as a mixture of Z- and -isomers. The cyclopentene derivative 52 affords the spiro-pyrrolidinone 53, together with the cyclopentapiperidinone 54, the naphthylthio group being eliminated (Scheme 2)50. 

Since both oxidative splitting of the double bond and aldol condensation represent reliable and general reactions, their sequence serves as an efficient route for the transformation of readily available cyclohexene systems e.g. formed via the Diels-Alder reaction or Robinson annulation) into functionalized cyclopentene derivatives. This standard operational mode is extensively used in total syntheses. One of the numerous examples, the synthesis of helminthosporal 463, the sesquiterpenoid toxin of fungi, is shown in Scheme 2.150. In the initial phases of the synthesis, commercially available (—)-carvomenthone 464 was transformed into 465 via Michael reaction with methyl vinyl ketone to give 466 and subsequent intramolecular aldol condensation. 

Vinylcarbene is also regarded as an intermediate in the catalytic isomerization of cyclopropene in the presence of [CuCl P(OPh)3 ]. 3-Methyl-3-cyclopropylcyclopropene (83a) and 3,3 dicyclo-propylcyclopropene (83b) react with cyclopentene derivatives under die influence of CuCl/P(OPh)3 to yield cntfo-vinylcyclopropane derivatives (84 equation 37) in 55-72% yields. 3-Methoxycarbonyl-l-propylcyclopropene also reacts with noibomadiene in the presence of CuCl to give the corresponding vinylcarbene adducts in 60% yield. 

As expected ( )-l,4-dichlorobut-2-ene reacts differently from its (2Z)-isomer with methyl methyl-thiomethyl sulfoxide, and produces a vinylcyclopropane instead of the cyclopentene derivative (Scheme 83, entry b, compare to entry a). 

The substrates bearing an isopropenyl terminus undergo an intramolecular ene process and ensuing thermodynamically controlled oleflnic isomerization from 1,4- to 1,3-diene to afford 1,3-cyclohexadiene systems. On the other hand, cyclopentene derivatives are provided for the substrates bearing 2-methyl-1-propenyl terminus, whereas no oleflnic migration is observed (Scheme 19). 

The first models for asymmetric induction in [2 + 2] cycloadditions are ketimines derived from precursors such as (25), which react with both cyclic and acyclic alkenes to give adducts with high enantiomeric excesses. Full details have been reported on the regio- and stereo-specificity of the addition of dichloroketene to 1-substituted cyclohexenes. Methyl (phenylthiomethyl)-ketene (26) provides a further example of a ketene which, after cycloaddition to cyclopentadiene, undergoes facile opening of the cyclobutane that is thus formed to provide vicinally substituted cyclopentene derivatives. ... 

Zinc and Mercury.—A remarkable new C—C bond-forming reaction involves a high-yield trimolecular condensation between alkyl halides, activated alkenes, and carbonyl compounds promoted by Zn in MeCN [equation (1)]. Cyclic bifunctional products are obtained when halogeno-ketones react under these conditions with acrylonitrile or methyl acrylate. Cyclopentene derivatives are... 

Diketones are readily transformed to cycHc derivatives, such as cyclopentanones and furans. In this manner, the fragrance dihydrojasmone (3-meth5l-2-pentyl-2-cyclopenten-l-one) is prepared by the base-catalyzed aldol condensation of 2,5-undecanedione. 2,5-Undecanedione is itself prepared from heptanal and methyl vinyl ketone in the presence of thiazoHum salts (329). i7j -Jasmone can be similarly prepared (330,331). 

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