合成路线1

A new asymmetric synthesis of orlistat has been described: Reaction of the chiral aminoindanol (I) with octanoyl chloride (II) in pyridine gives the chiral ester (III), which is condensed with cinnamaldehyde (IV) by means of TiCl4, DIEA and Bu2BOTf in dichloromethane yielding, after chromatographic purification, the anti-aldol adduct (V). Hydrolysis of the chiral auxiliary of (V) with lithium hydroperoxide affords the beta-hydroxy acid (VI), which is protected as the 1,3-dioxan-4-one (VIII) by reaction with pivalaldehyde (VII), TMS-OTf and isopropoxytrimethylsilane (TMS-O-i-Pr). Ozonolysis of (VIII) with O3 in dichloromethane yields the aldehyde (IX), which is condensed with 1-nitrododecane (X) by means of TBAF in DMF to provide the nitroaldol (XI). The dehydration of (XI) with DCC and CuCl in hot acetonitrile gives the nitroalkene (XII), which is reduced with Zn/HOAc to oxime (XIII). Oxidative hydrolysis of (XIII) with ceric ammonium nitrate (CAN) and HNO3 yields diketone (XIV), which is hydrolyzed with HCl in THF providing the beta-hydroxy acid (XV). Esterification of (XV) with benzyl iodide and CsCO3 gives the benzyl ester (XVI), which is estereoselectively reduced with Me4NB(OAc)3H in HOAc/acetonitrile yielding the chiral anti-1,3-diol (XVII). The selective protection of (XVII) with TIPS-OTf and 2,6-lutidine affords the monosilylated ester (XVIII), which is treated with H2 over Pd(OH)2 in ethyl acetate/methanol to furnish the free beta-hydroxy acid (XIX). Cyclization of acid (XIX) by means of PhSO2Cl in pyridine affords the beta-lactone (XX), which is desilylated with TBAF and HOAc in THF giving lactone (XXI). Finally, lactone (XXI) is esterified under Mitsunobu conditions with N-formyl-L-leucine (XXII) by means of DIAD and PPh3 in THF.