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A full account of the total synthesis of (±)-cassumunins A–C – superior antioxidants and anti-inflammatory agents – is given. Two novel approaches were developed for synthesizing cassumunins. The total synthesis of cassumunins A and B was accomplished in five linear steps from a known aldehyde in good overall yields of 50 and 43%, respectively, featuring a cascade [3,3]-sigmatropic shift (the Claisen rearrangement) and Heck cross-coupling reaction. Consequently, the total synthesis of cassumunin C was accomplished in three linear steps from a known alcohol with an overall yield of 53%. The key features involved in this synthesis are tandem [3,3]-sigmatropic shift, SN 2′ reaction, and aldol condensation. Moreover, a total of eighteen symmetrical and unsymmetrical curcumin analogues were synthesized. [ABSTRACT FROM AUTHOR]

A selective debromination of tetracyclic dibrominated bis-γ- lactones in the presence of triethylamine and mesyl chloride is reported. Both mesyl chloride and triethylamine are essential for the debromination process. The reduction is proposed to proceed through halophilic substitution of electrophilic bromine. The source of the halophile in this reaction is believed to be triethyl(mesyl)ammonium chloride. The nonoccurrence of debromination in dibromo bis-γ-lactones with tosyl chloride and triethylamine as reagents suggests that the formation of a source of well-dissociated chloride ions during the reaction is necessary. Furthermore, selective debromination of dibrominated bis-γ-lactones was also achieved by using pyridine-thionyl chloride as a reagent. Alternatively, potassium chloride-[18-crown-6] was demonstrated to be a suitable source of chloride ion for the reduction of bromolactones. [ABSTRACT FROM AUTHOR]

A racemic cyclopentannulated pyrrolidine derivative was synthesized utilizing ruthenium oxidation and borane reduction as the key steps. Ruthenium oxidation reaction of the 1,2-dibromoalkene moiety in an N-Boc-protected tetrabromonorbornyl derivative afforded a tricyclic α-hydroxy ketone, which on alkaline hydrogen peroxide cleavage furnished a bicyclic lactam in excellent yield. Borane reduction of the N-Boc-protected bicyclic lactam gave an unexpected product as a single diastereomer resulting from the reduction of not only the lactam and ester moieties but also the ketal to the corresponding methyl ether. A plausible mechanism involving an oxocarbenium ion is discussed. [ABSTRACT FROM AUTHOR]