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Cyclohexanone trans-6-alkylation

Structurally rigid substrate surrogates were added to the cubic section model before more flexible molecules as the following order signifies pentacyclic, tetracyclic, tricyclic, bicyclic ketones, trans/cis-decalones, methyl cyclohexanones and alkyl cyclohexanones. The hydroxyls of cyclohexanols were oriented axially with respect to cyclohexyl rings consistent with the Jones protocol and with the obsen/ation that... [Pg.498]

Bei der elektrochemischen Reduktion von Cycloalkanonen steht i. a. der stereochemi-sche Aspekt (cis/trans axial/aquatorial) im Vordergrund, so z. B. bei der Reduktion der Methyl- und anderer Alkyl-cyclohexanone, substituierter 2-Oxo-bicyclo[2.2.1]heptane und bei Oxo-dekalinen. Mit zumeist Alkoholen als Solvens fallen die entsprechenden cy-clischen sekundaren Alkohole zu 47-60% d.Th. an7-11. [Pg.605]

For simple, conformationally biased cyclohexanone enolates such as that from 4-t-butylcyclohexanone, there is little steric differentiation. The alkylation product is a nearly 1 1 mixture of the cis and trans isomers. [Pg.25]

Reductive alkylation of carboxamides 262 with sodium borohydride in the presence of an oxo compound furnished the carboxamides 265. In this process for the cis or trans isomers of 262 with acetone or cyclohexanone, the quinazolinone intermediates 266 [R = R = Me R, R = (CH2)s] of the reductive alkylation were also isolated and characterized [87-ACSA(B)228 91AX(C)2632]. [Pg.389]

The development of conditions for stoichiometric formation of both kinetically and thermodynamically controlled enolates has permitted the extensive use of enolate alkylation reactions in multistep synthesis of complex molecules. One aspect of the reaction which is crucial in many cases is the stereoselectivity. The alkylation step has a stereoelectronic preference for approach of the electrophile perpendicular to the plane of the enolate, since the electrons which are involved in bond formation are the n electrons. A major factor in determining the stereoselectivity of ketone enolate alkylations is the difference in steric hindrance on the two faces of the enolate. The electrophile will approach from the less hindered of the two faces, and the degree of stereoselectivity depends upon the steric differentiation. For simple, conformationally based cyclohexanone enolates such as that from 4 - /- b u ty I eye I o h cx an o ne, there is little steric differentiation. The alkylation product is a nearly 1 1 mixture of the cis and trans isomers. [Pg.17]

Although reasonable asymmetric induction has been observed in the alkylation of a chiral cyclohexanone enamine, it was noted1 in 1977 that in order to obtain higher induction in this type of reaction. Clearly what is needed is an amine with a C2 axis of symmetry . (+ )-trans-... [Pg.858]

Epoxide opening gives the needed trans isomer. Reduction of an alkylated cyclohexanone gives mostly the cis. [Pg.455]

This topological rule readily explained the reaction product 211 (>90% stereoselectivity) of open-chain nitroolefins 209 with open-chain enamines 210. Seebach and Golinski have further pointed out that several condensation reactions can also be rationalized by using this approach (a) cyclopropane formation from olefin and carbene, (b) Wittig reaction with aldehydes yielding cis olefins, (c) trans-dialkyl oxirane from alkylidene triphenylarsane and aldehydes, (d) ketenes and cyclopentadiene 2+2-addition, le) (E)-silyl-nitronate and aldehydes, (f) syn and anti-Li and B-enolates of ketones, esters, amides and aldehydes, (g) Z-allylboranes and aldehydes, (h) E-alkyl-borane or E-allylchromium derivatives and aldehydes, (i) enamine from cyclohexanone and cinnamic aldehyde, (j) E-enamines and E-nitroolefins and finally, (k) enamines from cycloalkanones and styryl sulfone. [Pg.323]

Scheme VII /19. A free radical mediated ring expansion of ds and trans a-alkylated /i-stanny-lated cyclohexanones [49] [50]. Scheme VII /19. A free radical mediated ring expansion of ds and trans a-alkylated /i-stanny-lated cyclohexanones [49] [50].
Asymmetric Alkylations and Michael Additions. Asym-metne alkylation of the cyclohexanone enamine derived from (+)-tran.s-2,5-dimethylpyrrolidine has been studied (eq 4). Alkylation with lodomethane, n-propyl bromide, and Allyl Bromide afforded the corresponding 2-n-alkylcyclohexanones in yields of 50-80% and with enantiomeric purities of 66, 86, and 64%, respectively. [Pg.287]

The nitration of enol acetates with acetyl nitrate is a regiospecific electrophilic addition to the 3-carbon of the enol acetate, followed by a hydrolytic conversion of the intermediate to the a-nitro ketone. With enol acetates of substituted cyclohexanones the stereochemistry is kinetically established. So, 1-acetoxy-4-methylcyclohexene (22) yields the thermodynamically less stable rrans-4-methyl-2-nitrocylo-hexanone (24) in greater proportion cis. trans = 40 60) (equation 8). This mixture can be equilibrated in favor of the thermodynamically more stable cis diastereomer (23) (cis. trans = 85 15). Nitration of 1-ace-toxy-3-methylcyclohexene (25) leads to frans-3-methyl-2-nitrocyclohexanone (26), which is also the thermodynamically more stable isomer (equation 9). No stereoselection occurs in the kinetically controlled nitration with acetyl nitrate of l-acetoxy-5-methylcyclohexene (27 equation 10), but the 1 1 mixture of the 5-methyl-2-nitrocyclohexanones can be equilibrated in favor of the trcms diastereomer (28) (cis trans = 10 90). 2-Alkyl-2-nitrocyclohexanones cannot be prepared in acceptable yields by nitration of the corresponding enol acetates with acetyl nitrate. [Pg.106]

Whitesell and Felman therefore concluded that an amine with a C2 axis of symmetry was required in order to ensure that the same side of the cyclohexene ring was shielded from attack whichever conformation of the enamine underwent alkylation. The en-antioselectivity was thereby considerably increased, but in the opposite chiral sense, by using the cyclohexanone enamine derived from ( + )-/mnj-2,5-dimethylpyrrolidine. This was assumed to have the S, S-configuration based on the results of the alkylation (Scheme 70). Optical yields of 82-93% ee were obtained. Also noteworthy was the low level of dialkylation observed (4-7%) and the fact that formation of enamine 77 was at least ten times faster using type 3A molecular sieves compared to 4A molecular sieves. Similar methodology has been applied to the alkylation of 4-substituted cyclohexanone enamines to give mainly the less stable trans disubstituted cyclohexanone s . [Pg.775]

Several highly hindered trialkylborohydrides, which are discussed in the section on alkyl-substituted cyclohexanones (see Section 2.3.3.1.2.2.1.), have been applied to 2-melhylcyclopen-tanone. In general, the results were very similar to those with 2-methylcyclohexanone (see Table 9), i.e., almost exclusive attack of the face of the carbonyl trans to the methyl group, leading to the ciis-alcohol. [Pg.725]

Five- and six-membered ring enolates with an endocyclic double bond also react to deliver an electrophile from the sterically less hindered face. Enolate 498 was obtained by treatment of 497 with lithium amide. Subsequent reaction with an alkyl halide led to delivery of the halide from the face opposite the alkenyl group (path a) and the trans product shown (499) was isolated in 60% yield.-. Approach via path b would have serious steric consequences, and that transition state is destabilized. Similar effects are observed with 3-alkyl-cyclohexanone derivatives. [Pg.789]

Further extent of asymmetric Sjvl a-alkylation methodology to ketone motifs was disclosed by Cheng and co-workers [129] in 2010. They described the first asymmetric catalytic direct a-alkylation of cyclic ketones catalyzed by functionalized chiral ionic liquids, namely proline-derived catalyst containing benzoimida-zolium moiety (LXI, Figure 8.1), and Brpnsted acid (TFA or phthalic acid). Moreover, described catalytic system enables asymmetric desymmetiization of 3-and 4-substituted cyclohexanones to afford 2,4-trans- and 2,5-cis-substituted products, respectively, with up to 99% yield, greater than 99 1 dr and good enantioselectivities (up to 87% ee). [Pg.293]


See other pages where Cyclohexanone trans-6-alkylation is mentioned: [Pg.111]    [Pg.132]    [Pg.76]    [Pg.1459]    [Pg.142]    [Pg.146]    [Pg.775]    [Pg.369]    [Pg.726]    [Pg.384]    [Pg.15]    [Pg.15]    [Pg.17]    [Pg.613]    [Pg.317]    [Pg.281]    [Pg.305]    [Pg.725]    [Pg.218]    [Pg.228]    [Pg.19]    [Pg.56]    [Pg.673]    [Pg.209]    [Pg.161]    [Pg.22]    [Pg.100]    [Pg.726]    [Pg.206]    [Pg.215]    [Pg.383]   
See also in sourсe #XX -- [ Pg.12 ]

See also in sourсe #XX -- [ Pg.12 ]




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