Reactions of Acid Chlorides/Ketenes with 2‐Substituted 4,5‐Dihydro‐4,4‐dimethyl‐1,3‐thiazoles: Formation of Penam Derivatives

Addition reactions of acid chlorides with various 2-substituted 4,5-dihydro-4,4-dimethyl-5-(methylsulfanyl)-1,3-thiazoles under basic conditions were studied. Two kinds of products were obtained from these additions, -lactams and non--lactam adducts. When the reaction was carried out with 4,5-dihydro-1,3-thiazoles with a Ph substituent at C(2), the reaction proceeded via formal [2+2] cycloaddition and led to the correspoding -lactam. On the other hand, acid chlorides and 4,5-dihydro-1,3-thiazoles bearing an -H-atom at the C(2)-substituent underwent C()- and/or N-addition reactions and furnished non--lactam adducts, i.e., C()- and/or N-acylated 1,3-thiazolidines. The attempted transformations of sulfonyl esters of exo-6-hydroxy penams to endo-6-azido penams failed, although they were successful with mono--lactams under the same conditions.