合成路线1

Indolizinone (I) was converted to the cyclic ketal (III) upon treatment with 2,2-dimethyl-1,3-propanediol (II) in the presence of p-toluenesulfonic acid. Carbethoxylation of (III) with diethyl carbonate and NaH afforded ester (IV), which was halogenated with either bromine or N-chlorosuccinimide to produce the corresponding alpha-bromo (V) or alpha-chloro (VI) ester, respectively. Sulfonylation of (R)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (VII) with 4-biphenylylsulfonyl chloride (VIII) provided the chiral auxiliary (IX). This was then condensed with halo ester (V) or (VI) in the presence of K2CO3 to furnish adduct (X). Diastereoselective alkylation of the sodium enolate of (X) with ethyl iodide produced (XI) as the major isomer. The cyano group of (XI) was then converted to acetamide (XII) by catalytic hydrogenation over Raney nickel in the presence of Ac2O and HOAc. Subsequent nitrosation of amide (XII) with NaNO2 in Ac2O/HOAc gave acetate ester (XIII).