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DOI: 10.1055/s-2002-33328
Hetero Diels-Alder
Reactions of Nitroso Alkenes with Alkoxyallene
Derivatives
Bearing Carbohydrate Auxiliaries: Asymmetric Synthesis
of
6H-1,2-Oxazines and Subsequent Reductive
Transformations
Publication History
Received
10 April 2002
Publication Date:
23 August 2002 (online)


Abstract
Alkoxyallene derivatives 1a-f bearing carbohydrate auxiliaries at the oxygen were examined in asymmetric hetero Diels-Alder reactions with nitroso alkenes. Diacetoneglucose derived compound 1a turned out to be the best precursor furnishing the primary cycloadducts 3a-c with a diastereomeric ratio of approximately 90:10. Isomerization provided the thermodynamically more stable 6H-1,2-oxazines 4a-c. Similarly, diacetonefructose derived allene 1f gave compounds 4h-j with good efficiency. Gratifyingly, it turned out that 1a and 1f were complementary with respect to the preferential absolute configuration at C-6 of 6H-1,2-oxazines 4a-c and 4h-j, respectively. Cycloadducts derived from 1a have 6S configuration in excess whereas those derived from 1f are predominantly 6R configured. Exhaustive hydrogenolysis of 6H-1,2-oxazines 4a and 4h in the presence of palladium on charcoal furnished the expected primary amine 5 in an enantioenriched form. If this reduction was performed under addition of hydrochloric acid, pyrrolidine derivative 6 together with secondary amine 7 as side product were isolated.
Key words
allenes - carbohydrates - asymmetric synthesis - hetero Diels-Alder reaction - 6H-1,2-oxazines - reduction - pyrrolidines