Abstract:
A Lewis acid induced intramolecular Diels-Alder (IMDA) reaction is used as the key step in the formation of symbioimine, an iminium alkaloid. The intermediate octahydronaphthalene is obtained from the IMDA reaction, after which extension of the aldehyde to a nitrile, alkylation of the nitrile, and imine formation allows for an efficient route to the target compound.
The enantioselective total synthesis of (+)-neosymbioimine was accomplished in 18 steps from (-)-(S)-citronellol utilizing an organocatalytic á-oxidation. The carbon core was constructed by a tandem Horner-Wadsworth-Emmons (HWE) reaction and an intramolecular Diels-Alder cyclization. All double bonds of Diels-Alder substrate were made in a stereoselective manner by Wittig-type reactions. Selective formation of the monosulfate monoester was accomplished by one-pot excessive sulfation followed by kinetic hydrolysis of bissulfate 18 in 79% yield.
A concise formal synthesis of platencin was based on an efficient oxygen-mediated palladium-catalyzed cycloalkenylation to form a bicyclo[3.2.1]octane, and a deoxygenative rearrangement of tosylhydrazone to construct the bicyclo[2.2.2]octane. The total yield of the core structure 6-3 of platencin was 17.5 % for 13 steps from a commercially available compound.