Cyclohexane-1,3-dione enol ethers

A new synthesis of ( )-lycoramine (40) (dihydrogalanthamine) has been reported by Schultz and co-workers (Scheme 4). The epoxide (33) was obtained from cyclohexane-1,3-dione enol ether (32) in five high-yield stages. The aryl ring was then introduced by base-catalysed reaction of the epoxide with 5-carbo-methoxy-2-methoxyphenol two isomeric enones (36) and (37) were formed,... 

Ethyl a-(bromomethyl)acrylate has proved to be an excellent reagent for conversion of aldehydes and ketones, both acyclic and cyclic, into the corresponding a-methylene-y-butyrolactone derivatives4"9 in a Re-formatsky type reaction. The yield was excellent in the case of several spiro a-methylene-y-butyrolactones.10 Synthetic a-methylene-y-butyrolactone derivatives have been shown to possess antitumor activity.5 6,7 1112 Ethyl a-(bromomethyl)acrylate has also proven of value in the synthesis of alkylated products of enol ethers of cyclohexane-1,3-dione.13... 

The otherwise rather difficult carbon alkylation of cyclohexane - 1,3-diones may be achieved photochemically although in rather variable yield, by irradiation through pyrex of a benzene solution of the dione and an enol ether, the alkyl portion of which is transferred [equation (53)l.1 ... 

The bis(silyloxy)cyclohexadienes (35) and (36) are prepared by treatment of the readily available keto trialkylsilyl enol ethers with lithium di-isopropylamide and chlorotrimethylsilane. The isomeric compound (37) is prepared by treatment of cyclohexane-1,4-dione with triethylamine, zinc(ii) chloride, and chlorotrimethylsilane. 

Ring cleavage of the enol ether (167) has been achieved by hydrolytic nitrosa-tion to give the oxime (168), which is easily converted into the corresponding ketone.Another rearrangement route to macrolides occurs in the reaction of the hydroxyketone (169) with base (Scheme 83) the macrolides (170) are obtained after removal of the benzenesulphonyl group. A related fragmentation of disubstituted cyclohexane-1,3-diones leads to macrolides but mixtures of products are sometimes obtained. ° ... 

A case in point is cyclohexane-1,3-dione. This may be converted into a mono-dioxolan [227, 228], or into a mono-dithiolem or -oxathiolan [228]. The dioxolan is partially cleaved to the hydroxyethyl enol ether (with which it is in thermal equilibrium) by very dilute base, and it reverts to the diketone under more strongly alkaline conditions [227]. The free ketone group in these ketals can be made to react vtith various nucleophilic reagents such as phenyl lithium [228] and cyanide ion [227] and can also be subjected to the Reformatski reaction [227], but the yields in these reactions appear to be rather low. 

The corresponding enol ether from cyclohexane>l,2 dione is obtained in the same way from the hydrated diketone dimer as obtained from the nitric acid oxidation of cyclo-hexanol this enol ether was used in a Refoimatski reaction... 

This conjugated ketone is prepared from cyclohexane-1,3-dione (1) via the enol ethyl ether (2), which is prepared by azeotropic distillation of a solution of (1)... 

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