A Michael Addition Approach Towards a Thienamycin Synthesis

Abstract

<p>A number of 2-aryl, 2-alkyl-4-[(E and Z]-1-alkoxyethyl-idene]-5-oxazolones, 2-alkylthio-4-[(E and Z)-1-alkoxyethyl-idene]-5-thiazolones and 2-ethoxy-4-[(E and Z)-1-ethoxyethyl-idene]-5-thiazolone were prepared. The configurations of the E and Z isomers of these compounds were assigned on the basis of the X-ray crystal structure of 4-[(Z)-1-ethoxyethylidene)-2-phenyl-5-oxazolone and by ¹H and ¹³C chemical shift data. These compounds were studied for reactivity to nucleophiles and electrophiles. Substitution reactions on the alkoxyethylidene portion of these compounds were effected with nitrogen, oxygen and suIfur nucleophiles and reaction with ring positions of 4-[(Z)-1-ethoxyethylidene]-2-phenyl-5-oxazolone and 2-ethoxy-4-[(Z)-1-ethoxyethylidene]-5-thiazolone gave ethyl 2-benzamido-3-ethoxy-2-butenoate and 4-[(Z)-1-ethoxyethylidene]-2,5-thiazolidinedione. The later product was ring opened to give ethyl 3-ethoxy-2-[N-methyl(methylthioamido)]-2-butenoate.</p> <p>Dienolate anions of many of the 4-(1-alkoxyethylidene)-5-oxazolones and corresponding thiazolones were prepared by removal of an allylic proton. These anions reacted with methyl 2-(chloromethylene)-3-oxobutanoate in a Michael reaction. The resulting 4-(1-alkoxy-4-carbomethoxy-5-hydroxy-2,4-hexadienylidene)-5-oxazolones and thiazolones were found to be susceptible to cyclization to the corresponding 4-(5-carbomethoxy-6-methyl-2-pyranylidene)-5-oxazolones and thiazolones.</p> <p>The dienolate anion of 4-[(Z)-1-ethoxyethylidene]-2-phenyl-5-oxazolone, was found to undergo Michael addition reactions with methyl 2- (chloromethylene)-3-oxobutanoate, methyl 2-(methoxymethylene)-3-oxobutanoate and ethyl 2-(phenylthio)-propenoate but not with ethyl 2-(phenylsulfinyl)propenoate, methyl (Z)-3-bromopropenoate and methyl (E)-3-chloropropoenoate.</p>