1 -Trimethylsiloxy-1 -cyclohexene

Diastereofacial differentiation occurs upon cyclopropanation of the substituted oyclohexene 43 with methyl diazoacetate. Only the two stereoisomers endo-44 and exo-44 were found, both with a 5-anti methyl group 60). In contrast, the ring substituents in l-trimethylsiloxy-cyclohexenes 45 and 46 are not efficient for such a differentiation, so that the four possible diastereomers are actually formed. 

Das ziemlich einfach herstellbare 1 -Hydroxy- 1-piperidino-cyclopropan kann in Gegen-wart von Titan(IV)-chlorid in einer Variante der Mannich-Reaktion als Aquivalent von Cyclopropanon/Piperidin dienen nach der anzunehmenden in-situ-Umwandlung in 1-Cyclopropyliden-piperidinium-chlorid erfolgen Reaktionen z.B. mit 1-Trimethylsiloxy-cyclohexen zu 2-Oxo-l-(l-piperidino-cyclopropyl)-cyclohexan (63%) und mit 1-Methyl-pyrrol bzw. Indol zu l-Methyl-2-( 1-piperidino-cyclopropyl)-pyrrol (65%) bzw. 3-(l-Pipe-ridino-cyclopropyl)-indol (84%)2 ... 

Nitration of 2-methyl-l-(trimethylsiloxy)cyclohexene (31) with nitronium tetrafluoroborate leads to 2-methyl-2-nitrocyclohexanone (32 equation 12), while 6-methyl-l-(trimethylsiloxy)cyclohexene (33) gives under similar conditions a 30 70 mixture of cis- and fran5-6-methyl-2-nitrocyclohexanone (equation 13). The desilylative nitration of allylsilanes with nitronium tetrafluoroborate proceeds readily. The reaction is considered to pass through initial electrophilic attack of the nitronium ion on the allyl system followed by desilylative elimination. So, on treatment of l-(trimethylsilyl)but-2-ene (34) with nitronium tetrafluoroborate the product is 3-nitrobut-l-ene (35) and not l-nitrobut-2-ene (equation 14). ... 

The cyclohexylidene ketal has been prepared from dimethoxycyclohexane and TsOH HC(OEt)3, cyclohexanone, TsOH,EtOAc, heat, 5h, 78% l-(trimethylsiloxy)-cyclohexene, coned. HCl, 20°C, 10-30 min, 70-75% yield, cyclohexanone, TsOH, CUSO4/ , and 1-ethoxycyclohexene, TsOH, DMF. The cyclohexylidene derivative of a fra .v-l,2-diol has been prepared. Cyclohexylidene ketals may also be prepared directly from an epoxide with MTO catalysis. ... 

The use of the Ln(OTf)3 in the activation of aldehydes other than formaldehyde was also investigated (Kobayashi and Hachiya 1992). The model reaction of 1-trimethylsiloxy-cyclohexene (2) with benzaldehyde under the influence of a catalytic amount of Yb(OTf)3 (10mol%) was examined. The reaction proceeded smoothly in H2O-THF (1 4), but the yields were low when water or THF was used alone. Among several Ln(OTf)3 screened, neodymium triflate (Nd(OTf)3), gadolinium triflate (Gd(OTf)3), Yb(OTf)3, and lutetium triflate (Lu(OTf)3) were quite effective, while the yield of the desired aldol adduct was lower in the presence of lanthanum triflate (La(OTf)3), praseodymium triflate (Pr(OTf)3) or thulium triflate (Tm(OTf)3) (table 2). 

Pyrrole ring. Ene-l,2-di(oxysilanes) can be used in place of acyloins for the synthesis of various heterocyclics. - E l,2-Bis(trimethylsiloxy)cyclohexene, ethyl /9-aminocrotonate, and glacial acetic acid heated 1 hr. at 100° ethyl 4,5,6,7-tetrahydro-2-methylindole-3-carboxylate. Y 96%. F. e. and heterocyclics s. K. Riihlmann et al., J. pr. 311, 844 (1969). 

The reactions of 1-TMS-cyclohexene oxide are similar (112). Treatment78,82 with sulfuric acid/water (in acetone), concentrated hydrobromic acid, sulfuric acid/ methanol, lithium aluminum hydride afford the corresponding compounds 1,2-di-hydroxy- (113)-, l-bromo-2-hydroxy- (114)-, l-methoxy-2-hydroxy- (115)-, 1-hydroxy-2-TMS-cyclohexane (117). Application of base to 115 yields 1-methoxy-l-cyclohexene (116). Pyrolysis of 112 gives a mixture of 1-trimethylsiloxy-l-cyclo-hexene (118) and 3-trimethylsiloxy-1-cyclohexene (ii9)77 (Scheme 13). 

Similarly, cyclohexene-3-one (162) gives in the first step l-trimethylsiloxy-3-TMS-l-cyclohexene (163) and by subsequent hydrolysis 3-TMS-cyclohexanone (264)108. If acetone is used instead, the system 242/Li/THF leads to 2-trimethyl-siloxy-2-TMS-propane (167) and after water treatment to 2-TMS-2-propanol (168)los ... 

Moreover, the formation of enoxy-silanes via silylation of ketones127 by means of N-methyl-N-TMS-acetamide (1 72) in presence of sodium trimethylsilanolate (173) was reported in 1969 and since then, the use of silylating reagents in presence of a catalyst has found wide appreciation and growing utilization as shown in recent papers128-132 (Scheme 27). Diacetyl (181) can be converted by trifluoromethylsul-fonic acid-TMS-ester (182) into 2,3-bis(trimethylsiloxy)-l, 3-butadiene (7treatment with ethyl TMS acetate (7 5)/tetrakis(n-butyl)amine fluoride l-trimethylsiloxy-2-methyl-styrene (i<56)130. Cyclohexanone reacts with the combination dimethyl-TMS-amine (18 7)/p-toluenesulfonic acid to 1-trimethylsiloxy-l-cyclohexene (iSS)131. Similarly, acetylacetone plus phenyl-triethylsilyl-sulfide (189) afford 2-triethylsiloxy-2-pentene-4-one (790)132. ... 

If 1-trimethylsiloxy-l-cyclohexene (193) is treated with borane/THF, hydrogen peroxide/alkali and then hydrolyzed, trans-l,2-cyclohexanediol (203) is obtained137 but trans-1 -hydroxy-2-trimethylsiloxycyclohexane (202) can be isolated without subsequent acid-catalyzed hydrolysis138 whereas the direct hydrolysis of the borane adduct 204 leads directly to cyclohexene (205)139K Very interesting is the use of TiCLt as catalyst. 193 plus benzaldehyde and TCI4 gives after hydrolysis 2-[hydroxy-(phenylmethyl)] cyclohexane-1-one (206)l40 ... 

The Mukaiyama aldol reaction of l-(trimethylsiloxy)-l-cyclohexene and benzalde-hyde has also been effected with the bidentate 188, giving the aldol products (erythro/ threo 1 3) in 87 % yield, though its monodentate counterpart 190 showed no evidence of reaction under similar conditions (Sch. 145). 

Trapping of the Beckmann intermediates with enol silyl ethers affords facile entry to a variety of en-amino ketones. This condensation takes place with retention of regiochemical integrity in both oxime sulfonates and enol silyl ethers. Reaction of 6-methyl-l-(trimethylsiloxy)-l-cyclohexene (41) or 1-methyl-2-(trimethylsiloxy)-l-cyclohexene (42) with cyclohexanone oxime mesylate furnishes (43) or (44), respectively, as the sole isolable products (equation 25). Another striking feature of the reaction is the high chemospecificity. The condensation of the enol silyl ether (45), derived from p-acetoxyaceto-phenone, occurs in a chemospecific fashion with cyclododecanone oxime mesylate, the acetoxy moiety remaining intact (equation 26). Oxime sulfonates of aromatic ketones and cyclopentanones are not employable since complex reaction mixtures are formed. 

Under the catalytic action of palladium(O) complexes, (2-siloxyallyl) acetates and the vinylogous [4-(trimethylsiloxy)penta-2,4-dienyl] acetate (Table 18), (2-oxo-3-silylpropyl) acetates (1-acetoxy-3-silylpropan-2-ones), ° and (2-oxoalkyl) carbonates react with the strained, but otherwise nonactivated double bonds in norbornene, norbornadiene, and dicyclopentadiene to form polycyclic cyclopropyl ketones, see also formation of 1, 2 °and 3. In contrast, the (2-siloxyallyl) acetates failed to react with simple alkenes such as dec-1-ene and cyclohexene. " With the substrates mentioned, the exo anti) diastereomers were obtained exclusively. 

Analogously to conventional reactions 201-203), bis(trimethylsiloxy) alkenes form heterocycles of different classes l,2-bis(trimethylsiloxy)-l-cyclohexene (305) reacts with formamide urea malodinitrile and ethyl (J-amino-crotonate to afford 4,5,6,7-tetrahydrobenzunidazole (309) ° 2-oxo-l, 3,4,5,6,7-hexahydrobenzimidazoIe (317) , 2-aniino-3-cyano-4,5,6,7-tetra-hydro-coumarone (312) and 2-methyl-3-ethoxy-carbonyl-4,5,6,7-tetrahydro-in-dole (373) respectively. 

The procedure works well when cyclohexene, cyclooctene, 2,2-dimethyl-3-(trimethylsiloxy)-3-butene and 1-phenyl-l-(trimethylsiloxy)ethylene are used as the olefin partner. Incorporation of oxygen gives the trioxanes in yields of 45-80%. 

Bidentate Lewis acid. This useful catalyst (1) with a high propensity for double coordination of the carbonyl group is prepared from the corresponding phenol and two equivalents of McjAI in CH Clj at room temperature. It catalyzes the reduction of 5-nonanone by BujSnH at -78° in 86% yield, whereas a reaction in the presence of the monodentate 0-dimethylaluminum 2,6-xylenoxide affords 5-nonanol in only 6%.. Accordingly, different catalytic efficiencies are also found in the Mukaiyama aldol reaction (e.g., 87% vs. 0% in the reaction between 1-trimethylsiloxy-l-cyclohexene and benzaldehyde) and the Claisen rearrangement of (fil-cinnamyl vinyl ether (96% vs. 0%). The contrasting ( >Zi-selectivity of the Michael adducts also reflects the different coordination states. 

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