2- Butanone, 4- cyclohexyl

In contrast, highly stereoselective aldol reactions are feasible when the boron etiolates of the mandelic acid derived ketones (/ )- and (5,)-l- t,r -butyldimethylsiloxy-l-cyclohexyl-2-butanone react with aldehydes33. When these ketones are treated with dialkylboryl triflate, there is exclusive formation of the (Z)-enolates. Subsequent addition to aldehydes leads to the formation of the iyn-adducts whose ratio is 100 1 in optimized cases. 

Surprisingly, the size of the silyl protecting group significantly influences the stereochemical outcome of aldol additions performed with the lithium enolates of (S )-l-trimethylsiloxy-and (S)-l-f< rt-butyldimethylsiloxy-l-cyclohexyl-2-butanone. Thus, the former reagent attacks benzaldehyde preferably from the Si-face (9 1), which is the opposite topicity to that found in the addition of the corresponding titanium enolates of either ketone ... 

The chlorotitanium enolate, generated by treatment of (S )-l-tm-butyldimethylsiloxy-l-cyclohexyl-2-butanone with titanium(iv) chloride and diisopropylethylamine, provides the syn-product upon reaction with benzaldehyde. The diastereoselectivity of 99 1 is defined as the ratio of the major isomer to the sum of all other isomers47bc. 

Both the titanium4, d and the lithium enolate47c of (S)-l-benzoyl-l-cyclohexyl-2-butanone deliver the srn-aldol 6c, predominantly. 

Treatment of 2 -anilinofluorans with ketones such as acetone or 2-butanone in hydrochloric acid in the presence of iron(III) chloride gives 4,4 -alkylidenebis(A-fluoran-2-ylaniline)s. Thus, 2 -anilino-6 -(A-cyclohexyl-/V-methylainino)-3 -methylfluoran, (86) is treated with acetone in hydrochloric acid in the presence of iron(III) chloride to give 2,2-bis(4-[6 -(N-cy c 1 o hexyl-Ar-methy 1 amino)-3 -methylfluoran-2 -ylamino]phenyl (propane (87)60 (Eq. 9). 

Enantioselective reduction of simple aliphatic ketones is one of the most challenging of the currently unresolved problems in this field. The Rh/4 complex catalyzed the hydrosilylation of 2-butanone with diphenylsilane at 0 °C, which after hydrolysis gave (S)-2-butanol in 56% ee (Scheme 3) [17]. 2-Octanone and 4-phenyl-2-butanone were reduced with diphenylsilane in the presence of the cationic Rh/EtTRAP-H at -50 °C and gave optical yields of 77% and 81%, respectively [12], The cationic Rh/(R,R)-t-Bu-MiniPHOS was also effective for the reduction of 4-phenyl-2-butanone with 1-naphthylphenylsilane at -20 °C, affording the R product in 80% ee [13]. 3-Methyl-2-butanone was reduced using the Rh/4 complex with 76% optical yield [17]. Hydrosilylation of cyclohexyl methyl ketone with the Rh/(R,S)-2 complex followed by hydrolysis afforded the R alcohol in 87% ee [8]. Highly enantioselective hydrosilylation of pinacolone with diphenylsilane at -20 °C was achieved by means of the Rh/4 complex and yielded the desired R product in 95% ee [17]. 

Dimethyl-1-cyclohexyl-1-trimethylsiloxy-ethene (191) gives by means of methyllithium/ethylbromide in dimethoxyethane (DME) 1-cyclohexyl-2,2-dimethyl-1-butanone (297)133 Dimerizations occur when substances such as 1-trimethylsiloxy-styrene (192) or 1-trimethylsiloxy-l-cyclopentene (195) are treated with silver oxide/ DMSO to afford l,5-diphenyl-2,5-butadione (198) and 2,2 -dicyclopentanonyl (199)l34 respectively. Under the catalytic influence of Cu2+ ions, 192 plus ben-zenesulfonyl chloride yield phenyl-(l-phenyl-l-ethanone-2-yl)sulfone (200)l3 ... 

Titanium-Catalyzed Epoxidations of 4-Cyclohexyl-4-hydroxy-3-metliylene-2-butanone Typical Procedure32 ... 

To a cold (0 °C) solution of 0.2 g (1.1 mmol) of 4-cyclohexyl-4-hydroxy-3-methylene-2-butanone dissolved in 8 mL of dry benzene is added 0.06 g (0.22 mmol) of vanadyl acetylacetonate, producing a green solution which is stirred for 20 min before dropwise addition of 0.73 mL (2.2 mmol) of 3 M r-BuOOH in 2,2,4-trimethylpentane over 10 min. The resultant red solution is stirred for 10 h at r.t. and the color changes to yellow-brown. The reaction mixture is washed with 4 mL of H20, 4 mL of brine and dried over MgS04. Evaporation of the solvent in vacuo followed by column chromatography (silica gel, petroleum ether/EtOAc 3 1) gives 0.16 g (76%) of pure yyrc-epoxide. 

Cram s rule12fi or the more recent model of Felkin127 can be employed to predict the stereochemical outcome of such reactions. However, Meerwein-Ponndorf-Verley reductions present some of the few exceptions to the rule. For example, (-)-(R)-3-cyclohexyl-2-butanone is, in contrast to prediction, predominantly reduced by aluminum isopropoxide to the corresponding eryf/iro-product128. 

Predict the position of acid-catalyzed bromination of each of the following ketones (a) 2-butanone, (b) 2-pentanone, (c) 3-methyl-2-butanone, (d) 2-methylcyclohexanone, and (e) methyl cyclohexyl ketone. 

It did not predict the correct product when 3-cyclohexyl-2-butanone was reduced by aluminum isopropoxide, however. Cram, D. J. Greene, F. D. ]. Am. Chem. Soc. 1953, 75, 6005. 

Cram s model does not always predict the stereochemical result of kinetically controlled reductions with aluminum isopropoxide (Cram and Greene, 1953). For example, i -(—)-3-cyclohexyl-2-butanone is reduced to predominantly ZR,2R-erythro carbinol (erythro/threo = 1.9). Apparently special steric forces are important in this reduction. Recent work (Shiner and Whittaker, 1963) has shown that aluminum isopropoxide is trimeric or tet-rameric. It is therefore conceivable that some hydride transfers will involve Al(OR)3 units that are not coordinated to the carbonyl groups they reduce. These transfers may occur preferentially from the side opposite that exposed to a coordinated Al(OR).3 unit. Such competitive mechanistic pathways might well yield an isomer ratio not in agreement with that produced by less complex reducing agents. 

Signicant new information related to the photodecomposition of some bifiinctional alkyl nitrates has been reported. In addition to absorption spectra of many alkyl nitrates, Roberts and Fajer (1989) also measured the spectra for the bifiinctional 2-nitrooxyethanol. Bames et al. (1993) studied the absorption spectra and photolysis products of several dinitrates 1,2-propandiol dinitrate, 1,2-butandiol dinitrate, 2,3-butandiol dinitrate, l,4-dinitrooxy-2-butene, 3,4-dinitrooxy-l-butene, as well as several bifiinctional nitrates a-nitrooxyacetone, l-nitrooxy-2-butanone, and 3-nitrooxy-2-butanone. Wangberg et al. (1996) reported on the the atmospheric chemistry of the bifiinctional cycloalkyl nitrates 2-hydroxy-cyclopentyl-l-nitrate, 2-oxo-cyclohexyl-1-nitrate, and frans -l-methyl-cycto-l,2-dinitrate. In this section, we will review the findings related to the tropospheric photodecomposition of these multifunctional nitrates. 

H = 3-nitrooxy-2-butanone (Barnes et al., 1993) / = 2-oxo-cyclohexyl-l-nitrate J = fra i-l-methyl-cyclohexyl-l,2-dinitrate (Wangberg et al., 1996) K = 2-nitrooxyethanol (Roberts and Fajer, 1989)... 

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