Solavetivone, synthesis

The spiroketone (347), previously used as an intermediate in the synthesis of several vetispirane sesquiterpenoids (cf. Vol. 5, p. 79) has been converted into ( )-solavetivone (337) by the sequence of reactions shown in Scheme 31. ... 

Solavetivone (661) has also been a synthetic objective with two new syntheses having been completed. The first of these (Scheme 63) achieved syntheses of both solavetivone (661) and the hydroxy derivative (675), whose glucoside has been identified in tobacco.302 The second synthesis (Scheme 64) relied upon a Diels-Alder reaction to construct a bicyclo[2,2,2]octyl framework which was then cleaved by acid to release a prenyl-mesylate (679) for further acid-promoted... 

The reaction of trimethylaluminum [65,66] with cyclohexadienone was also catalyzed by the combination of the oxazoline ligand 28 and copper(I) triflate to afford relatively high selectivity (Scheme 15) [67]. The process was successfully applied to the asymmetric total synthesis of (-)-solavetivone [68]. 

A synthetically useful example of this process is the conversion of 117 to 120, which involves a 1,2-alkyl shift, and was part of Hwu s synthesis of (-)-solavetivone. 38 jhe alkyl fragment is actually part of the bicyclic ling system, one arm of the bicyclo[4.4.0]decane ring system. Reaction of the OH unit with the Lewis acid resulted in formation of the tertiary cation 118, which was followed by a 1,2-alkyls shift to give 119, where the new cation is stabilized by the adjacent silicon of the trimethylsilyl group. 39 Loss of the trimethylsilyl group from 119 gives spiran (120). 

Efficient synthesis of ( ) sativene and ( ) solavetivone have appeared. Both routes involve the alkylation of a vinylogous ester, methoxycyclopentenone in the former case and 5-methyl-3-methoxycyclohexenone in the latter case, the follow this with an intramolecular Diels-Alder reaction. 

An intramolecular cycloaddition of an a diazoketone, a reaction which has featured prominently this year, forms the key step, (250) - (251), in a synthesis of solavetivone. By contrast, intramolecular cycloadditions of car-benoids derived from a-diazoketones have been used in total synthesis of ( )-a-chamigrene and (-)-acorenone B in the latter case, (+)-limonene was used as the chiral precursor. ... 

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