Silyl cyclopentene

Bercaw has investigated the application of the 6 2-symmetric, enantiomerically pure lanthanide metallocene derivative (i ,A)-BnBpYH 34 as a catalyst for the asymmetric cyclization/hydrosilylation of 1,5- and 1,6-dienes. Although 34 displayed high activity for the reaction of a number of dienes, asymmetric induction was low. In the best case, reaction of 3,3-dimethyl-1,5-hexadiene with phenylsilane catalyzed by 34 gave silylated cyclopentene 35 in 95% yield with 50% ee (Equation (25)). 

Butyn-2-one undergoes tandem [3+2] cycloadditions of allyltriisopropylsilane to give a bicyclo[3.3.0]octane as a mixture of three possible diastereomers in a good yield (Scheme 10.169) [468]. The use of a reduced amount of the allylsilane forms a silylated cyclopentene as a minor product. This indicates that the 1 1 cycloadduct is the precursor of the bicyclic product. In contrast, the ZnL or Me2AlCl-promoted reaction of 3-butyn-2-one with an isocyclic allyltrimethylsilane affords a [2+2] adduct wifhout [3+2] adducts [448a, 469] (vide infra). 

The Danheiser annulation, in its classic form, is the Lewis acid-catalyzed reaction of an a,yff-unsaturated ketone 1 with a trimethylsilylallene 2 to form a silyl cyclopentene 3. More broadly, the Danheiser annulation ecompasses reactions of silylallenes 4 with electrophilic double bonds to form cyclic products 5, usually under Lewis acid catalysis. The Danheiser annulation should not be confused with other annulation processes developed by Danheiser, such as Danheiser s aromatic annulation and the Stork-Danheiser alkylation. ... 

H3C)3SiCl 3-(Chloro) cyclopentene 12h at 20 C in tetra-hydrofuran 3-(trimethyl- silyl) cyclopentene 94 140-146 79... 

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]. 

In order to establish the correct absolute stereochemistry in cyclopentanoid 123 (Scheme 10.11), a chirality transfer strategy was employed with aldehyde 117, obtained from (S)-(-)-limonene (Scheme 10.11). A modified procedure for the conversion of (S)-(-)-limonene to cyclopentene 117 (58 % from limonene) was used [58], and aldehyde 117 was reduced with diisobutylaluminium hydride (DIBAL) (quant.) and alkylated to provide tributylstannane ether 118. This compound underwent a Still-Wittig rearrangement upon treatment with n-butyl lithium (n-BuLi) to yield 119 (75 %, two steps) [59]. The extent to which the chirality transfer was successful was deemed quantitative on the basis of conversion of alcohol 119 to its (+)-(9-methyI mande I ic acid ester and subsequent analysis of optical purity. The ozonolysis (70 %) of 119, protection of the free alcohol as the silyl ether (85 %), and reduction of the ketone with DIBAL (quant.) gave alcohol 120. Elimination of the alcohol in 120 with phosphorus oxychloride-pyridine... 

Photocycloaddition of cyclopentene (116) to the trimethylsilyl ether (117) gave 2 stereoisomers (118) and (119). When (118) was reduced with LiAlH4 in Et20, followed by treatment will MsCl, pyridine and dimethylaminopyridine (DMAP), the silyl ether (120) was obtained. Finally, (120) was allowed ro react with KF in the presence of [18]-crown-6 in CH2C12, as a result, hexahydroazulenone (121) was isolated41 >. On the other hand, the cyclobutane (119) could also be converted similarly to (121) in an overall yield of 47 % 41K... 

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. 

This reaction is extended to the intramolecular ring closure of the intermediate radical 224 with olefinic or trimethylsilylacetylenic side chains [121]. Cu(BF4)2 is also effective as an oxidant (Scheme 89) [122]. Conjugate addition of Grignard reagents to 2-cyclopenten-l-one followed by cyclopropanation of the resulting silyl enol ethers gives the substituted cyclopropyl silyl ethers, which are oxidized to 4-substituted-2-cyclohexen-l-ones according to the above-mentioned method [123]. (Scheme 88 and 89)... 

Trans-1 -allyl-2-(trimethylsilyl)cyclopentane and trans-1 -allyl-2-(trimethylsilyl)-cyclohexane are formed from the reaction of la with cyclopentene and cyclohexene, respectively. A second allylsilylation reaction of these compounds with la also gives unusual allylsilylation products, 7-cyclopent-l-enyl-2,2-dimethyl-4-(trimethylsilyl-methyl)-2-silaheptane (30%) and 4-((cyclohex-l-enyl)methyl)-2,2,8,8-tetramethyl-2,8-disilanonane (39%). As observed in the allylsilylation of 4-(trimethylsilyl-methyl)-l-alkenes, these products are likely formed via intramolecular silyl rearrangements. In this case, the results strongly suggest that a 1,5-silyl shift and... 

The authors describe a control experiment in which CTOss-benzoin product 245 was subjected to standard reaction conditions with achiral triazolium pre-catalyst 191 yielding retro-benzoin products, as well as cyclopentene product 247 Eq. 24. This result additionally demonstrates the reversibility of the benzoin reaction. When trimethylsilyl-protected 245 is treated under the same reaction conditions with ethanol as a nucleophile, ketoester 248 is formed along with retro silyl-benzoin and Stetter products. This result provides enough evidence that the cross-benzoin/oxy-Cope mechanism cannot be dismissed. 

Ojima has reported a rhodium-catalyzed protocol for the disilylative cyclization of diynes with hydrosilanes to form alkylidene cyclopentanes and/or cyclopentenes. As an example, reaction of dipropargylhexylamine with triethyl-silane catalyzed by Rh(acac)(GO)2 under an atmosphere of CO at 65 °G for 10 h gave an 83 17 mixture of the disilylated alkylidene pyrrolidine derivative 92b (X = N-//-hexyl) and the disilylated dihydro-1/ -pyrrole 92c (X = N-//-hexyl) in 76% combined yield (Equation (60)). Compounds 92b and 92c were presumably formed via hydrosilyla-tion and hydrosilylation/isomerization, respectively, of the initially formed silylated dialkylidene cyclopentane 92a (Equation (60)). The 92b 92c ratio was substrate dependent. Rhodium-catalyzed disilylative cyclization of dipro-pargyl ether formed the disilylated alkylidene tetrahydrofuran 92b (X = O) as the exclusive product in low yield, whereas the reaction of dimethyl dipropargylmalonate formed cyclopentene 92c [X = C(C02Et)2] as the exclusive product in 74% isolated yield (Equation (60)). 

Triazines are generally more reactive in [2 + 4] cycloaddition in comparison with 1,2,3-tria-zines. The wide variety of dienophiles can be employed enamines, enaminones, vinyl silyl ethers, vinyl thioethers, cyclic ketene jV,O-acetals, /V-phenylmaleimide, 6-dimethylaminopentafulvene, 2-alkylidene-imidazolidines (cychc ketene aminals), cyclic vinyl ethers, arynes, benzocyclopropene, acetylenes, and alkenes like ethylene, (Z)-but-2-ene, cyclopentene, cyclooctene and bicyclo[2.2.1]hept-2-ene, hexa-1,5-diene, cycloocta-1,5-diene, diallyl ether, cyclododeca-l,5,9-triene,... 

Allenylsilanes react with a,p-unsaturated acylsilanes to give trimethylsilyl-sub-stituted cyclopentenes (equation I) the reaction of allenylsilanes with a-methyl-a,p-unsaturated acylsilanes results in silyl-substituted cyclohexenones.2... 

Ozonolysis of silyl ethers of l-cyclopenten-3-ol gives a high selectivity in favor of the exo-substituted ozonide48. The bulkier silyl blocking groups, as shown in entry 37 of Table 1, exhibit a somewhat higher degree of stereo selection. Furthermore, the size of the... 

Asymmetric hydrosilylation of cyclopentadiene with HSiCl3 catalyzed by a Pd complex of (Sj-f/ -ferrocenylphosphine (240, Rf = C3F7) proceeds in a 1,4-manner to give 3-silyl-1-cyclopentene (239, X = Cl) with up to 60% ee (R) (equation 93)246. The same reaction using (5,)-2-(A-methanesulfonylamino)-3-methyl-l-diphenylphosphinobutane (241) and HSiMeCF yields 239 (X = Me) with up to 71% ee (S) (equation 93)245. In a similar manner, the reaction of 1,3-cyclohexadiene with HSiF2Ph catalyzed by (/ )-(5 )-l-diphenylphosphino-2-(l-acetoxyethyl)ferrocene (PPF-OAc) affords (,S )-3-silyl-l-cyclohexene (242) with 77% ee (equation 94)247. 

Cyclopentene annelation. The known rearrangement of vinyl cyclopropanes to cyclopentenes (cf. 7, 190 9, 83, 265) can be used to obtain silyl-substituted cyclopentenes. The precursors, (l-trimethylsilylcyclopropyl)ethylenes (2), are usually prepared by addition of 1 to an aldehyde or a ketone followed by cyclopropanation (C2HjZnI, CH2I2) of the adduct. The products are then dehydrated by TsOH to 2 (equation I).1... 

These silyl-substituted vinyl cyclopropanes are stable to acid but rearrange thermally to silyl-substituted cyclopentenes in which the double bond occupies the more substituted position.2 Example ... 

Carboxylates behave as an O-nucleophile and are allylated. Reaction of AcONa with cyclopentadiene monoxide (139) proceeds with retention of stereochemistry as shown by 140, to give the 3,5-c -disubstituted cyclopentene 141 [74], Although alcohols are rather unreactive nucleophiles for the Pd-catalysed allylation, the alkoxide anions generated by the treatment of silyl ethers with TBSF are easily allylated. Desilylated alcohol from 142 reacts intramolecularly with the cis and trans vinyl epoxides to give the cis and trans pyrans 143 and 144 regio- and stereoselectively, and... 

Recently, Barton and coworkers investigated the mechanism of the 1,2-silyl migration in a related system through a combination of experiment and theory40. Pyrolysis of 12 at 600 °C cleanly produced a mixture of 12 and methylenedisilacyclopentene 13 (25%) (equation 12). A kinetic study of this reaction was conducted over the temperature range of 520-600 °C in a stirred flow reactor. The Arrehnius parameters for the first order formation of 13 were logA = 12.5 s-1 and Ea = 54 kcalmol-1. In the pyrolysis of a related all-carbon system 14, decomposition occurred at 550 °C but no isomerization to the methylene cyclopentene 15 was observed up to 700 °C (equation 13). 

Allenylated silyl enolates such as 6-siloxy-l,2,5-trienes and 5-siloxy-l,2,5-trienes undergo W(CO)6-catalyzed 5- and 6-OTr/o-cyclizations to give the corresponding cyclopentenes and cyclohexenes, respectively (Equation (85)).315 These cyclizations proceed via electrophilic activation of the allene moiety by coordination of W(CO)s photochemically generated from W(CO)6-... 

The vinylcyclopropane to cyclopentene rearrangement is seemingly broadly applicable to solution of the five-ring annulation problem. Besides the example cited in Scheme 8, routes provided by Trost,61 Miller,62a and Conia62b are conceptually attractive. Thus, we see that reaction of a cyclopentanone with the cyclopro-pyldiphenylsulfonium ylide provides an oxaspiropentane which can be opened efficiently with an amide base (Scheme 10). The resulting silylated cyclopropanol can be... 

---