Procedure:Compound ( 1 ) (0.65 mol) is added dropwise to a stirred solution of N 2 0 4 (1 I g, 0.13mol) in dry ether (40ml) cooled to -10°C. After 1 hour's stirring at -5"C, excess N r 0 4 and ether are removed ina vacuum.-Isolation of (2): The precipitate is rapidly filtered off and washed with a small volume of ice-cold ether.-Preparation of (3): The reaction mixture is stirred for 20min with water (30ml), then taken up in benzene, and the benzene phase is washed neutral with water, dried with M g S 0 4 and evaporated in a Rotavapor. The crystalline residue is filtered, washed with a small amount of ice-cold light petroleum, and recrystallized from the same solvent.
112.0 g of butyl 6ct-fluoro-ll p-hydroxy-16a-methy1-3,20dioxo-l,4-pregnadien-21-oate ( 3 c).
Procedure B :A solution of (3c) (5.0g) in n-propanol (300ml) is refluxed with potassium tert-butoxide (250mg) under argon for 1 h. The product is precipitated with 1% acetic acid, filtered off, dried, and recrystallized from acetonehexane. One obtains 2.07g of propyl 6a-fluoro-I 1 ~-hydroxy-16~-methy1-3,20-dioxo-1,4pregnadien-21-oate (39).
Wir fanden jetzt, daD die praparativ leicht zuganglichen 1,l-Ditert.-butylallene ( ideale Ausgangsverbindungen zur Synthese von 3-substituierten 4,4-Di-tert.-butyl-4H-1,2-oxazet-Noxiden sind. Addition von N,04 an (1) fiihrt nach dem Aufarbeiten bei Raumtemperatur direkt zu den gut kristallisierenden Oxazet-N-oxiden (3). Bei vorsichtigem Aufarbeiten bei ca. 0°C lassen sich die Dinitroalkene (2) isolieren, die beim Erwarmen glatt in Reaktionen 1. Ordnungzu (3) cyclisieren. ( a ) , R = H; (b), R = Br; ( c ) . R = C 1
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