4- tert-Butylcyclohexanone: Cyclohexanone, 4-

Triethylamine (8) Ethanamine, N,N-diethyl- (9) (121-44-8) 4-tert-Butylcyclohexanone Cyclohexanone, 4-terf-butyl- (8) Cyclohexanone, 4-(l,l-dimethylethyl)- (9) (98-53-3)... 

In contrast, the tin(Il) enolates of cyclohexanone undergo addition to (2f)-(2-nitroethenyl)ben-zene to give 2-(2-nitro-l-phenylethyl)cyclohexanones with high anti diastereoselection5. The analogous reactions with cyclopentanone and 4-tert-butylcyclohexanone were less diastereose-lective with anti/syn ratios of 70 30 and 62 38. respectively. Modest to excellent diastereoselec-tivity was observed with acyclic ketones (d.r. 75 25 to 90 10) however the precise stereochemical details were not provided. 

Surprisingly, the bulkiness of the 4-substituent on the phenol ring did not have a significant influence on the cis/trans ratio of the formed alkylcyclohexylamines at the same reaction conditions, whereas a bulky substituent in 2-position made the reduction of the intermediate cyclohexanone more difficult. After one hour of reaction time, 2-tert. butylcyclohexanone was the only product formed. Prolonged reaction led to the slow formation of 2-alkylcyclo-hexanols. In the case of the methoxy-substituted phenol, hydrogenolysis of the ether group took place. 

With other less-rigid cyclohexanones, the stereochemical course of the reduction is less easy to predict. In general, a mixture of products is obtained in which, with comparatively unhindered ketones, the more stable equatorial alcohol predominates with hindered ketones, the axial alcohol is often the main product. Thus, reduction of 4-tert-butylcyclohexanone 84 with lithium aluminium hydride gives predominantly the equatorial trans-4-/ crt-butylcyclohexanol, whereas the hindered 3,3,5-trimethylcyclohexanone 85 gives a mixture containing mainly the axial alcohol 86 (7.69,7.70). The latter is almost the only product when a more hindered and hence more selective reducing agent such as L-selectride [LiBH( Bu)3] or lithium hydrido-tri-tert-butoxyaluminate [LiAlH(0 Bu)3] is employed. 

Cyclic and bicyclic ketones such as cyclohexanone, 2-methylcyclohexanone, 4-tert-butylcyclohexanone, and norcamphor undergo complete reduction in 30-60 min. Hindered ketones, like diisopropyl ketone and camphor, need 6-12... 

The extreme buUdness of these aluminum reagents is able to control the addition reaction of carbonyl compounds by complexation which will or can lead to unexpected stereoselectivity. When MAD was mixed with the carbonyl compound of 4-tert-butylcyclohexanone, a stable 1 1 complex was formed. This complex was treated with methyllithium at low temperature to yield an equatorial alcohol almost exclusively. The observed stereochemical outcome was opposite that of the product from reaction of cyclohexanone with methyllithium. The equatorial selectivity achieved with MAD was found to be almost perfect [11, 12], Furthermore, if the same reaction conditions are applied to chiral aldehydes, a fi-Felkin selectivities are observed [12] (Scheme 5). 

When zeolite MCM-22 is employed as catalyst for the reaction between substituted cyclohexanones and sec-alcohols, instead of the MPV reduction obtained with Beta, a novel reductive etherification occurs to give, for example, from 4-tcrt-butylcyclohexanone and i-PrOH the isopropyl ether of 4-tert-butylcyclohexa-nol with a cisitrans isomer ratio of 60 40 [34]. It is considered that in this reaction the higher Brpnsted-acid site population relative to MPV sites favors the formation of the ether via an intermediate hemiacetal. 

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