The ability to undergo [4 + 2] versus [2 + 2] cycloaddition was under investigation for ketenes thermally generated from carbamoyl Meldrum's acid. Usually, 1,3‐oxazino‐5‐carbamoylo‐4,6‐diones are formed when carbamoyl Meldrum's acid reacts with imine. However, in some cases, a reaction takes an unexpected course, leading to the formation of tetraponerines alkaloids derivatives or cyclic iminoethers.
Acyl ketenes formed during thermal decomposition of 5-acyl-2,2-dimethyl-1,3-dioxa-4,6-diones undergo stereoselective [2+2] cycloaddition to chiral aldimines.
An efficient practical synthetic procedure has been developed for the synthesis of 2,2-dimethyl-5-{aryl[(hetero)aryl]methyl}-1,3-dioxane-4,6-diones through Friedel-Crafts alkylation. The scope and limitation of the reaction of 2,2-dimethyl-5-arylidene-1,3-dioxane-4,6-diones with π-excess aromatic systems have been delineated.
A new process for the stereoselective formation of 3‐acyl‐β‐lactams using 5‐[hydroxy‐(phenyl/1‐naphthylmethyl)methylene] ‐2,2‐dimethyl‐1,3‐dioxa‐4,6‐diones and chiral aldimines under pyrolytic conditions is developed.
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