RESUMO
The dihydrobenzoxazone 9e, which is easily prepared from salicylamide 11 and cyclohexanone, serves as an efficient auxiliary in the synthesis of the 1-beta-methylcarbapenem key intermediate 10. The stereocontrolled Reformatsky-type reactions of the acetoxyazetidinone 2 with the carboximides 6 gave the intermediates 7 with high diastereoselectivities in high chemical yields. The auxiliary 9e also acts as a good leaving group in the TMSCl-promoted Dieckmann-type cyclization leading to a 1-beta-methylcarbapenem skeleton. By using this auxiliary, 10 was synthesized in 58% overall yield and four steps from 2.
RESUMO
Cis- and trans-isomers of alpha-hydroxy-alpha,beta-dibenzyl-gamma-butyrolactone lignans 1a,d-g and 2a,c,d were stereoselectively synthesized in good yields based on the electrophilic addition to the metal enolate of alpha-benzyl-gamma-butyrolactone derivatives 1l-o and 3 as a key step. This method was applied to the syntheses of (+/-)-trachelogenin and (+/-)-guayadequiol, representative examples of the trans- and cis-isomers of alpha-hydroxy-alpha,beta-dibenzyl-gamma-butyrolactone lignan series.
RESUMO
Novel syntheses of the 1beta-alkylcarbapenems were achieved on the basis of Eschenmoser sulfide contraction via the new bicyclic 1,3-thiazinone intermediates. 1,3-Thiazinones 7, 16, and 25 were effectively prepared from thioesters 5 and 22 using a C4-S bond formation process. The sulfide contraction reactions were performed by treatment of 7, 16, and 25 with base (NaH or KO-t-Bu) in the presence of triphenylphosphine to generate the corresponding carbapenem enolate 12, 17, and 26, which were trapped by (PhO)(2)POCl followed by the reaction with mercaptans to afford carbapenems 10a, 10b, 19, and 28, respectively.