合成路线1

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanylazetidinone (II), which by reaction with AgNO3 is converted into the silver salt (III). Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) ­ obtained by treatment of carboxylic acid (V) with thionyl chloride ­ to provide the azetidinone thioester (VI). Alternatively, compound (VI) can be obtained by condensation of tetrahydrofuran-2(R)-thiocarboxylic S-acid (VII) ­ obtained by treatment of carboxylic acid (V) with hydrogen sulfide ­ with silylated azetidinones (I) or (VIII) by means of NaOH in THF/water. Condensation of azetidinone thioester (VI) with allyl glyoxylate (IX) in refluxing benzene gives the hydroxy ester (X), which is treated with SOCl2 to yield the chloro ester (XI). Reaction of compound (XI) with triphenylphosphine and lutidine in hot THF provides the phosphoranylidene derivative (XII), which is converted into (5R,6S)-6-[1(R)-hydroxyethyl]-2-[2(R)-tetrahydrofuryl]penem-3-carboxylic acid allyl ester, faropenem allyl ester (XIII) by removal of the silyl protecting group with tetrabutylammonium fluoride, followed by cyclization in refluxing toluene. Compound (XII) can also be obtained by condensation of the silver salt of protected azetidinone (XIV) with tetrahydrofuran-2(R)-carbonyl chloride (V).