Highly stereocontrolled synthesis of the 1β-methylcarbapenem key intermediate by the reformatsky reaction of 3-(2-bromopropionyl)-2-oxazolidone derivatives with a 4-acetoxy-2-azetidinone
摘要:
The key synthetic intermediate (4) of 1-beta-methylcarbapenems (1 approximately 3) was efficiently synthesized by employing highly stereocontrolled Reformatsky reaction (C4-alkylation) of 3-(2-bromopropionyl)-2-oxazolidone derivatives (6) with (3R,4R)-4-acetoxy-3-[(R)-1-(t-butyldimethylsilyloxy)ethyl]-2-azetidinone (5) in the presence of zinc dust followed by removal of 2-oxazolidone moieties. The best diastereoselectivity (beta:alpha = 95.5) could be realized by uses of sterically crowded achiral 2-oxazolidone derivatives such as 4,4-dimethyl-, 4,4,5,5-tetramethyl, and 4,4-dibutyl-5,5-pentamethylene-2-oxazolidone and higher reaction temperatures (refluxing tetrahydrofran). The remarkable diastereoselectivities observed for the Reformatsky reactions could be explained by means of the weakly chelating transition state models.
A compound of the formula: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are each a hydrogen atom, a lower alkyl group, an ar(lower)alkyl group or an aryl group, or R.sub.1 and R.sub.2 may be combined together to form a lower alkylene group and/or R.sub.3 and R.sub.4 are combined together to form a lower alkylene group, or R.sub.1, R.sub.2, R.sub.3 and R.sub.4 may be combined together to form an o-phenylene group, X is a halogen atom and Y is an oxygen atom or a nitrogen atom substituted with lower alkyl or aryl, which is useful as an intermediate in the synthesis of 1.beta.-methylcarbapenem compounds valuable as antibiotics.
A highly stereoselective synthesis of a key intermediate of 1β-methylcarbapenems employing the reformatsky reaction of 3-(2-bromopropionyl)-2-oxazolidone derivatives