合成路线1

The reaction of L-tyrosine methyl ester (I) with ethyl chloroformate and K2CO3 in water gives the carbamate (II), which is protected with Bn-Br and K2CO3 in DMF, yielding the benzyl ether (III). The reduction of (III) by means of LiAlH4 in refluxing THF affords the chiral 2-methylaminopropanol (IV), which is protected as its Boc derivative (V) by means of Boc2O. The oxidation of (V) by means of DMP provides the carbaldehyde (VI), which is reductocondensed with glycine methyl ester (VII) by means of NaBH3CN in methanol to give the adduct (VIII). Elimination of the Boc protecting group of (VIII) by means of TFA yields the diamine (IX), which is cyclized by means of NH4OH in ethanol to afford the piperazinone (X). Elimination of the benzyl protecting group of (X) by hydrogenation with H2 over Pd/C provides the phenol (XIa)-(XIb), which is cyclized by means of bis(acetoxy)iodobenzene in hexafluoroisopropanol to give the spiranic cyclohexadienone (XII). The hydrogenation of (XII) by means of Tes-H and CuI in dichloromethane yields the spiranic cyclohexanone (XIII), which is finally ketalized by means of ethyleneglycol (XIV) and PPTS in refluxing benzene to provide the target ethyleneketal intermediate (XV) (See scheme no. 18599903a, intermediate (XV)).