Abstract
Starting from L-alanine, L-phenylalanine, L-leucine, L-norleucine, or L-isoleucine, 2-diazo-3-oxo- 4-phthalimido-alkanoates 8 were prepared in three steps. Considerable racemization occurred at the stage of the 3-oxo-4-phthalimido-alkanoates 7. Dirhodium tetraacetate effectively catalyzed the intramolecular formation of carbonyl ylides 9, which in the absence of a trapping reagent underwent a (3+3) cycloaddition reaction to form the dimers 10. Carbonyl ylides 9 underwent (3+2) cycloaddition reactions with several electron-deficient alkenes and alkynes to give oxygen and nitrogen containing multicyclic systems 12-16. The keto group of the α-oxy-β-ketoester moiety of cycloadducts 2 and 12 is easily hydrated to give the gem-diol.
Highlights
While carbenoid C,H insertion and olefin cyclopropanation reactions give rise to carbocyclic frameworks, various heterocyclic ring systems become accessible in the presence of additional heteroatom-containing functional groups being able to participate in carbenoid reactions
Since α-diazoketones and α-diazo-β-ketoesters are frequently synthesized from carboxylic acids as starting materials, it is not far-fetched to consider amino acids as precursors for diazocarbonyl compounds incorporating an additional amine functional group and eventually a chiral center, if the naturally occurring α-amino acids are considered
We report on the use of several α-alkyl-substituted, naturally occurring αamino acids as starting materials for the preparation of the title compounds structurally related to 1
Summary
The intramolecular metallocarbenoid chemistry of α-diazocarbonyl compounds has attracted much attention in recent years.[1,2] While carbenoid C,H insertion and olefin cyclopropanation reactions give rise to carbocyclic frameworks, various heterocyclic ring systems become accessible in the presence of additional heteroatom-containing functional groups being able to participate in carbenoid reactions. After chromatography with ethyl acetate–cyclohexane (1:2), 0.18 g (0.54 mmol, 14%) of an orange oil was obtained; mixture of two diastereomers
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