合成路线1

This compound is prepared by several related ways: 1) The reaction of silylated azetidinone (I) with tetrahydrofuran-2-thiocarboxylic acid (II) by means of NaOH in THF - water gives the azetidinone thioester (III), which is condensed with allyl glyoxylate in refluxing benzene yielding the hydroxyester (IV). The reaction of (IV) with SOCl2 affords the chloroester (V), which by reaction with triphenylphosphine by means of lutidine in hot THF is converted into the phosphoranylidene derivative (VI). The elimination of the silyl protecting group of (VI) with tetrabutylammonium fluoride gives the azetidinone (VII), which is cyclized in refluxing toluene yielding the (5R,6S)-6-[1(R)-hydroxyethyl]-2-[2(R)-tetrahydrofuryl]penem-3-carboxyli c acid allyl ester (VIII). Finally, this compound is hydrolyzed with triphenylphosphine, sodium 2-ethylhexanoate and Pd-tetrakis(triphenylphosphine). 2) The condensation of the silver salt of protected azetidinone (IX) with tetrahydrofuran-2(R)-carbonyl chloride (X) also yields the phosphoranylidene salt (VI). 3) Phosphoranylidene ester (VI) can also be cyclized first in refluxing benzene yielding the silylated penem ester (XI), which is deprotected with tetrabutylammonium fluoride to (VIII). 4) The hydrolysis of allyl ester (VIII) to the final product can also be performed with paladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethylacetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether. 5) The preceding hydrolysis can also be performed with triphenylphosphine and paladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone.