Chiral auxiliary menthone

Naturally occurring ketones and their readily prepared derivatives have also been used as chiral auxiliaries. Menthone ketals have been the subject of some study [373, 374], For example, enolates of compound 1.106, obtained from 8-phenylmenthone, are alkylated with a good stereoselectivity [375]. Cleavage of the chiral auxiliary is accomplished by hydrolysis. Enolates of tert-butylglycine camphor imine 1.107 are alkylated [154, 159] or suffer Michael additions [376] with a high stereoselectivity, and the auxiliary is cleaved by treatment of the prod-... 

Chapter 27. Recently Nokami discovered a highly efficient enantioselective allyl-transfer reaction catalyzed by Sn(OTf)2 or TsOH using (-)-menthone as a chiral auxiliary (c) Hussain, L, Koma-SALA, T, Ohga, M., Nokami, J. Synlett 2002, 640. (d) Nokami, J., Ohga, M., Nakamoto, H., Matsubara, T, Hussain, L, Kataoka, K. /. Am. Chem. Soc. 2001, 323,... 

An intemnolecular [2+2] cycloaddition using an enantiomerically pure enone substrate is described by M. Demuth. His menthone derived bicyclic acetal adds to cyclopentene with high diastereoselectivity (with both diastereoisomers obviously being enantiomerically pure). This chiral auxiliary also has been used in several syntheses of (+) and (-)-grandisol, a potent aggregation pheromone of the boll weevil. 

Lewis acid catalyzed aldol coupling of silyl enol ethers with substituted cyclohexanone acetals showed an excellent preference for equatorial attack (95-l(X)%). In accord with this general rule, additions of a silyl enol ether to equatorially or axially substituted chiral spiroketals derived from -menthone gave 00% equatorial attack and formation of a single one of the four possible diastereoisomers (Scheme 9) 3, 4 -pjjjg methodology, followed by protection of the hydroxy group (X = OTHP, (XIPh.i) and alkaline removal of the chiral auxiliary was used for the synthesis of several natural products. ... 

On this subject, eventually, Demuth has recently reported the shortest biomimetic synthesis of steroidal skeletons in enantiopure form [40], Using the photoinduced electron transfer (PET) technology, he examined the behavior of diastereomeric )-geranylgeranylmethyl 82 and 86 bearing a (—)-menthone-based chiral auxiliary. Irradiation of 82 provided the two diastereomers 83 and 84 in a 1 7 ratio, and in 10% yield (Scheme 25). The a -trans chair approach from the a-face (82-a+ ) appears much more favorable than that from the j8-face because of steric interactions with the chiral auxiliary. Enantiopure C-17-substituted steroid 85 was... 

Nokami reported a study that documents the asymmetric rearrangement of chiral oxonium ions (Scheme 16.19) [97]. These reactive intermediates are generated upon condensation of optically active alcohols and aldehydes. The requisite alcohol 158 was prepared by diastereoselective addition of cro-tylmagnesium chloride 156 to menthone 157. Subsequent treatment of the alcohol with an aldehyde such as PhSCH2CH2CHO under acidic conditions induced formation of 159. The ensuing [3,3]-rearrangement gave 160, and in situ hydrolysis of the chiral auxiliary afforded the secondary homoallylic alcohol with excellent optical purity (99% ee). 

An alternative approach was developed by the group of Demuth97, based on the intermolecular photoaddition of chiral l,3-dioxin-4-ones 192 and 194 possessing the (—)-menthone auxiliary that could smoothly be removed after the photoaddition step. The results of Demuth s pioneering studies into the reactions of chiral dioxinones with cyclic... 

DBU (1) effectively works in the isomerization of the condensation products from l-menthone with salicylamide, which could be a potential chiral 1,3-benzoxazinone auxiliary [65] (Scheme 3.39). 

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