Cyclopentenes 1-vinyl-1-cyclopentene

Hydrosilylation of I-vinyl-1-cyclohexene (77) proceeds stereoselectively to give the (Z)-l-ethylidene-2-silylcyclohexane 78, which is converted into (Z)-2-ethylidenecyclohe.xanol (79)[74]. Hydrosilylation of cyclopentadiene affords the 3-silylated 1-cyclopentene 80. which is an allylic silane and used for further transformations[75.75a]. Cyclization of the 1,3,8, lO-undecatetraene system in the di(2.4-pentadienyl)malonate 69 via hydrosilylation gives the cyclopentane derivative 81. which corresponds to 2.6-octadienylsilanc[l8,76]. 

The cyclohexadiene derivative 130 was obtained by the co-cyclization of DMAD with strained alkenes such as norbornene catalyzed by 75[63], However, the linear 2 1 adduct 131 of an alkene and DMAD was obtained selectively using bis(maleic anhydride)(norbornene)palladium (124)[64] as a cat-alyst[65], A similar reaction of allyl alcohol with DMAD is catalyzed by the catalyst 123 to give the linear adducts 132 and 133[66], Reaction of a vinyl ether with DMAD gives the cyclopentene derivatives 134 and 135 as 2 I adducts, and a cyclooctadiene derivative, although the selectivity is not high[67]. 

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). 

In a 200-ml three-necked flask fitted with a dropping funnel (drying tube) is placed a solution of 13.4 g (0.12 mole) of 1-octene in 35 ml of THF. The flask is flushed with nitrogen and 3.7 ml of a 0.5 M solution of diborane (0.012 mole of hydride) in THF is added to carry out the hydroboration. (See Chapter 4, Section I regarding preparation of diborane in THF.) After 1 hour, 1.8 ml (0.1 mole) of water is added, followed by 4.4 g (0.06 mole) of methyl vinyl ketone, and the mixture is stirred for 1 hour at room temperature. The solvent is removed, and the residue is dissolved in ether, dried, and distilled. 2-Dodecanone has bp 119710 mm, 24571 atm. (The product contains 15 % of 5-methyl-2-undecane.) The reaction sequence can be applied successfully to a variety of olefins including cyclopentene, cyclohexene, and norbornene. 

Vinyl-substituted cyclopropanes undergo thermal rearrangement to yield cyclopentenes. Propose a mechanism for the reaction, and identify the pericyclic process involved. 

Small amounts of cyclopentene derivatives are detected in cyclopropanation reactions of electron-deficient dienes, but they may result from thermal rearrangement of the corresponding vinyl cyclopropanes and not from a direct [4+1] cycloaddition... 

Dihydro-2iy-thiopyrans, derived from dimethylbuta-1,3-dienes, Na2S203-5H20 and various activated alkyl h des, ring contract on treatment with a strong base leading to vinyl cyclopropanes and cyclopentenes <96JOC4725>. 

The anions of vinyl cyclopropanols (16), conveniently released from ethers (15) with BuLi, rearrange rapidly to cyclopentenes (17). 

The use of the NHC-Ni catalytic system has also been used to promote the cycloisomerisation of vinyl cyclopropanes 125 to afford the cyclopentene rings 126 in excellent yields (Scheme 5.33) [38]. The reaction required only 1 mol% of [NiCCOD) ] and 2 mol% of IPr carbene. 

As for cyclopropanation of alkenes with aryldiazomethanes, there seems to be only one report of a successful reaction with a group 9 transition metal catalyst Rh2(OAc)4 promotes phenylcyclopropane formation with phenyldiazomethane, but satisfactory yields are obtained only with vinyl ethers 4S) (Scheme 2). Cis- and trans-stilbene as well as benzalazine represent by-products of these reactions, and Rh2(OAc)4 has to be used in an unusually high concentration because the azine inhibits its catalytic activity. With most monosubstituted alkenes of Scheme 2, a preference for the Z-cyclopropane is observed similarly, -selectivity in cyclopropanation of cyclopentene is found. These selectivities are the exact opposite to those obtained in reactions of ethyl diazoacetate with the same olefins 45). Furthermore, they are temperature-dependent for example, the cisjtrcms ratio for l-ethoxy-2-phenylcyclopropane increases with decreasing temperature. 

The 0/7/fo-alkylation of aromatic ketones with olefins can also be achieved by using the rhodium bis-olefin complex [C5Me5Rh(C2H3SiMe3)2] 2, as shown in Equation (9).7 This reaction is applied to a series of olefins (allyltrimethyl-silane, 1-pentene, norbornene, 2,2 -dimethyl-3-butene, cyclopentene, and vinyl ethyl ether) and aromatic ketones (benzophenone, 4,4 -dimethoxybenzophenone, 3,3 -bis(trifluoromethyl)benzophenone, dibenzosuberone, acetophenone, />-chloroacetophenone, and />-(trifluoromethyl)acetophenone). 

The complexes derived from 1-vinylated cyclopentene and cyclohexene undergo completely regio- and stereoselective reactions, as indicated in Scheme 13.12 [23],... 

Scheme 13.12. Allyltitanation of aldehydes from 1-vinylated cyclopentene and cyclohexene.

The extrapolation of the vinylcyclopropane-cyclopentene rearrangement to a vinyl-cyclobutaiie-cyclohexene synthesis begins to create new insights into the synthesis of six membered ring natural products. The eudesmane sesquiterpene (—)-P-selinene, 217 illustrates such a strategy as summarized in Scheme 14 80). A suitable cyclohexene... 

The results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

An interesting application was described by Liebeskind and Stone, who prepared l-(methoxy-l,2-propandienyl)-2-cyclobuten-l-ols 62 by treatment of cyclobutenones 61 with lithiated methoxyallene 42 (Scheme 8.16) [59]. The authors used these primary adducts in a subsequent acid-catalyzed ring-enlargement providing 5-hydroxy -5 -vinyl- 2 -cyclopenten-1 -ol s. 

A regioselective [3 + 2]-cycloaddition approach to substituted 5-membered carbo-cycles was made available by the use of allenylsilanes [188]. The reaction involves regioselective attack of an unsaturated ketone by (trimethylsilyl)allene at the 3-position. The resulting vinyl cation undergoes a 1,2-silyl migration. The isomeric vinyl cation is intercepted intramolecularly by the titanium enolate to produce a highly substituted (trimethylsilyl)cyclopentene derivative. 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

The submitters report that dimethyl 3-cyclopentene-1,1-dicarboxylate (with <1% of the vinyl isomer)2 3 can be isolated at this stage in 92% yield and then transformed to methyl 3-cyclopentene-1-carboxylate4 with lithium chloride in wet dimethyl sulfoxide (DMSO)5 in 85% yield. 

It will be noted that the isomerization to cyclopentene proceeds with a considerably lower energy of activation than the other cyclopropane isomerizations so far discussed. As a result these reactions have been investigated kinetically at temperatures about 100° lower than those not having a vinyl substituent. A number of substituted vinylcyclopropanes have been studied and the Arrhenius parameters for their isomerizations to substituted cyclopentenes determined. The results are shown in Table 4. From the results in Table 4 it can be seen that the isomerizations... 

Cyclohexanol, Cyclopentane, Cyclopentene, 1,2-Dichloroethane, Diethyl phthalate, 1,4-Dioxane, Ethephon. Ethylamine, Ethylene dibromide, Ethylenimine, p-Propiolactone, Tetraethyl pyrophosphate, TCDD, 1,1,1-Trichloroethane, Trichloroethylene, Vinyl chloride Ethylene chlorohydrin, see Bis(2-chloroethyl) ether Ethylenediamine, see Ethylene thiourea. Maneb Ethylene glycol, see Bis(2-chloroethyl) ether, 1,2-Dichloroethane, Ethylene chlorohydrin. Ethylene dibromide... 

Carbon tetrachloride. Chloroform, 2-Chlorophenol, Cyclohexanol, Cyclopentene, 1,1-Dichloroethylene, irans-l, 2-Dichloroethylene, IV.yV-Dimethylaniline, lV,lV-Dimethylformamide, 2,4-Dimethylphenol, 2,4-Dinitrotoluene, 1,4-Dioxane, 1,2-Diphenylhydrazine, Ethyl formate. Formaldehyde, Glycine, Methanol, Methylene chloride. Methyl formate, 2-Methvlphenol. Monuron, 4-Nitrophenol, Oxalic acid, Parathion, Pentachlorophenol, Phenol, l idine. Styrene, Trichloroethylene, Vinyl chloride Formylacetic acid, see cis-l,3-Dichloropropylene, irans-1,3-Dichloropropylene IV-Formylcarbamate of 1-naphthol, see Carbaryl Formyl chloride, see Chloroethane, Chloroform, sym-Dichloromethyl ether, ds-1,3-Dichloropropylene, irans-ES-Dichloropropylene, Methyl chloride. Methylene chloride. Trichloroethylene, Vinyl chloride lV-Formyl-4-chloro-o-toluidine, see Chlornhenamidine. 

A third mechanistically distinct [3 -1- 2] cycloaddition between vinyl ethers and vinyl-carbenoids was discovered and reported in 2001 [26]. This reaction is remarkable because when Rh2(S-DOSP)4 is used as the catalyst, the cis-cyclopentenes 142 are formed in up to 99% enantiomeric excess. The reaction occurs between vinylcarbenoids unsubstituted or alkyl-substituted at the vinyl terminus and vinyl ethers substituted with an aryl or vinyl group. Some illustrative examples are shown in Tab. 14.12. The reaction is considered to be a concerted process, which would be consistent with the highly stereoselective nature of the reaction [26]. Contrary to the [3-1-2] cycloaddition derived by means of vinylogous carbenoid reactivity, this latest [3 -1- 2] cycloaddition is not influenced by solvent effects. Due to steric demands on the carbenoid, the [3-1-2] cycloaddi-tion only occurs with cis-vinyl ethers. 

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