合成路线1

Hydrolysis of (5,5-ethylenedioxy-1-cyclohexenyl)acrylic acid (XVI) with p-TsOH followed by reductive amination with NH4OAc and NaBH3CN and N-acylation of the obtained amine with ethyl chloroformate (VIII) gives carbamate (XLI) as a racemic mixture, which is resolved by means of chiral HPLC, providing the (R)-enantiomer (XLII). Esterification of acid (XLII) with allylic alcohol (XXXII) in the presence of EDC and DMAP in CH2Cl2 yields the corresponding ester (XLIII), which by intramolecular Diels–Alder cyclization in xylene at 147 °C followed by epimerization in the presence of DBU furnishes the tricyclic intermediate (XLIV). Catalytic hydrogenation of alkene (XLIV) over Pt/C affords the saturated compound (XLV) , which is finally hydrolyzed with NaOH . Alternatively, condensation of nitro acid (XXXVII) with the hydroxypentynamide (XXX) by means of pivaloyl chloride, NMP and DMAP yields ester (XLVI), which is submitted to partial hydrogenation over Lindlar catalyst poisoned with quinoline to afford triene (XLVII). Thermal Diels–Alder cyclization of compound (XLVII) followed by epimerization in the presence of DBU provides the tricyclic carbamide (XLVIII). Simultaneous nitro group and olefin reduction in compound (XLVIII) by means of H2 and Pt/C or by transfer hydrogenation with HCOOH and Pd/C leads to the tricyclic amine (XLIX), which is finally acylated with ethyl chloroformate (VIII) to afford the corresponding carbamate (XLV) .
Other synthetic approaches to intermediate (X) include alkaline cleavage of benzothiazolyl ketone (L) (4) and hydrogenation/debenzylation of the unsaturated precursor (LI) over Pt/C .