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, β ‐lactams and non‐ β ‐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 β ‐lactam. On the other hand, acid chlorides and 4,5‐dihydro‐1,3‐thiazoles bearing an α ‐H‐atom at the C (2)‐substituent underwent C ( α )‐ and/or N ‐addition reactions and furnished non‐ β ‐lactam adducts, i.e., C ( α )‐ 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‐ β ‐lactams under the same conditions.