Stereoselectivity in formation of oxacephams from 1,3‐alkylidene‐threitols

Abstract

The [2+2]cycloaddition of CSI to the (Z)-propenyl ethers derived from respective 1,3-methylidene- and 1,3-ethylidene-threitols, contrary to the corresponding erythritol derivatives, is characterized by a low stereoselectivity and a lack of stereospecificity. On the other hand, the alternative method of the oxacepham formation, based on the 4-vinyloxy-azetidinone, proceeds with an excellent stereoselectivity. The CD-spectroscopy offers an attractive tool for determination of the absolute configuration of the bridgehead carbon atom at the 5-oxacepham skeleton.

Synthesis of 3-Substituted-clavams: Antifungal Properties, DD-Peptidase and β-Lactamase Inhibition

“…The (1R,3ЈR,4ЈR) configuration assigned for 26 and the ratio of 24 : 25 : 26 at Ϫ50°C indicated that the adduct 24 underwent epimerization at the stage of the N-chlorosulfonylated [2ϩ2]cycloadduct. Similar epimerization has also been noticed in the past [25].…”

Stereochemistry of the [2+2] Cycloaddition of Chlorosulfonyl Isocyanate to Chiral Alkoxyallenes Derived from 1,3‐Alkylidene‐L‐erythritol and ‐D‐threitol

“…In the case of threitols 19 and 20 the stereoselectivity of the formation of β-lactams 37, 38 and 39, 40 was much less satisfactory and amounted to 1:1 and 1.4:1, respectively. In comparison with the corresponding vinyl ethers 62 [15] and 63, [16] the cycloadditions giving alkoxyallenes 9, 10 and 19, 20 proceeded with a significantly lower stereoselectivity in both the erythritol and threitol series.…”