Epoxides, vinyl lithium chloride

Vinyl epoxides can also be ring-opened via an Sn2 sense, as exemplified in the macrocyclization of the epoxy-tethered cyclopentenone 76, which was induced to occur by treatment with lithium 2,2,6,6-tetramethylpiperidide (LTMP) followed by the mild Lewis acid diethylaluminum chloride in THF. The enolate attacked exclusively from the a-position of the... 

Two new preparations of 1,8-cineole (553) [the biogenesis of which from geraniol (25) in Rosmarinus officinalis has been elucidated ] have been recorded. A Diels-Alder adduct 625 (R = Me) of methyl vinyl ketone and isopropenyl methyl ketone was converted to the diazoketone (R = CH = N2) with diethyl oxalate/base, then toluenesulfonyl azide, and treatment of the latter with [Rh(OAc)2]2 in methylene chloride at room temperature for five minutes converted it in very high yield to the tricyclic compound 626. Lithium dimethylcuprate then yielded the ketone 627, conversion of which to 1,8-cineole (553) was known.The other 1,8-cineole synthesis was a by-product of an observation which enabled the two stereoisomers of limonene 1,2-epoxide to be separated. The cjs-epoxide 549 was brominated to stereoisomers of a dibromocineole 628, under conditions when the rran.s-epoxide did not react, and could be distilled pure afterward. The dibromo compound 628 yielded 1,8-cineole (553) with tributyltin hydride. 

It is noteworthy that in diethyl ether both the methyl and vinyl groups of (1) are transferred to C3 of 2-cyclopentenone. Also note that even in THF (1) undergoes coupUng reactions with acid chlorides and epoxides with preferential transfer of the methyl group. At the present time the selectivity of organic group transfer of mixed lithium dialkyl cuprates is not well understood. ... 

The organolithium reagent (1) also reacts with a wide variety of other electrophiles, including silyl chlorides to provide bis(silyl)methane derivatives, and nitriles to provide -sUyl amines after in situ reduction of the intermediate imine derivative. a-Silyl epoxides are opened to provide the substituted vinylsilane. Reaction of (1) with arenesulfonyl fluorides provides a-silyl sulfones, key intermediates for the preparation of vinyl sulfones. Reaction of the lithium reagent (1) with alu-... 

The stereochemical information is introduced by (J )-methyl p-toluenesulfoxide 110. This compound is deprotonated with lithium diisopropylamide and reacted with a-chloro methylacetate 109 to give a-chloroketone 111. This ketone when reacted with diisobutylaluminum hydride at —78°C gives (J )-chlorohydrine 112, whereas reaction of ketone 111 with diisobutylaluminum hydride and zinc chloride gives the corresponding (S)-chlorohydrine 113. Treatment of both chlorohydrines with potassium carbonate resulted in the formation of epoxides 114 and 116. These can now be reacted with either (Z)- or (T)-vinyl cuprates to give the desired homoallylic alcohols 115 and 117 in diastereomeric excesses around 90%. 

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