Enol Friedel-Crafts alkylation, reductive

A similar strategy was used by Fehr and co-workers to achieve the enantioselective (5,5)-vulcanolide (5, 5)-26 synthesis (Scheme 31.12). Li-enolate of ketone 33 was protonated by ( )-//-E affording the enantioenrichied ketone 34. Then, Friedel-Craft alkylation of o-xylene followed by reduction provides the secondary alcohol 35. The trans cyclohexyl derivative 36 was easily obtained under acidic conditions in 44% over three steps. Then, a monooxidation affords the (5,5)-vulcanolide (S,5)-26) in ca. 29% yield over five steps with 83% ee. 

Numerous new examples of cyclopentenone synthesis from acetylenehexacarbonyl-dicobalt complexes and norbornene derivatives have been disclosed there is evidence of steric control, and the bulky trimethylsilyl group can be employed as a removable direction-determining group to allow synthesis of 3- instead of 2-sub-stituted cyclopentenones. Reaction of (731) with sodamide in toluene gave the new octahydro-2,5-methanoazulene system (732 R = CONHj) successive hydrolysis, reduction, and esterification converted (732 R = CONHj) into (732 R = CHjOTs) which, on solvolysis, gave the homoprotoadamantane derivative (733 X = H, R R = CH2) in high yield.The carboxylic acid (732 R = COjH) underwent spontaneous Friedel-Crafts intramolecular acylation on conversion into its acid chloride to give (733 XX = O R R = CHj) and (733 XX = O, R = Cl, R = Me). Reaction of methyl a-bromocrotonate (mixture of E- and Z-isomers) with the enolates of cyclohex-2-enone affords a mixture of stereoisomeric tricyclo-[3,2,l,0 ]octan-6-ones (734 R —R are variously H or alkyl) in moderate yield. The reaction involves double Michael addition and subsequent substitution. 

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