Carvones Michael addition

HSCH2CH2SH, Zn(OTf)2 or Mg(OTf)2, CICH2CH2CI, heat, 16 h, 85-99% yield.o ,l3-Unsaturated ketones such as carvone are not cleanly converted to ketals because of Michael addition of the thiol. ... 

Michael addition of cyanide to both (+)- and (-)-carvone 1 has been studied in detail. All four possible products 2 can be obtained depending on the conditions, and it has been shown that 2 (P-CN, p-Me) is the kinetically controlled product, as first described by Lapworth in 1906. Reaction of 2 with pentyl nitrite in the presence of NaOEt/EtOH is strongly exothermic, and the temperature of the reaction mixture must be kept below 0°C. The product, formed in 62% yield, is the isoxazoloazepine 3. 

The double bonds of enones easily undergo Michael additions and this may be used for their temporary masking. Thus dimethylamine or, better, propanethioP may be added to the conjugated system. From the adducts thus formed, the alkene may finally be recovered via pyrolysis of the derived meth-iodide. In a recent development the silylcuprate derived fiom dimethylphenylsilyllithium and copper iodide is added to the -position of enones. The silyl ketones (107) produced in this way can conveniently be used for further syntheses. The double bond may be reobtained by bromination followed by desilylbromination (Scheme 101). The sequence was, for instance, successful in syntheses of carvone (108) and dehydrojasmone. 

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