Periodate, tetrapropylammonium, reaction with

Chiral nitrosoureas can be easily prepared starting from disubstituted pyrrolidines possessing C2 symmetry. Thus (27 , 57 l-dimcthyI pyrrolidine can be smoothly converted, by reaction with phenoxyhydroxamic acid in pyridine solution to the corresponding (V-hydroxyurea 1. Oxidation of 1 with tetrapropylammonium periodate in dichloromethane gives the short-lived nitroso dienophile 2 which reacts with 1,3-cyclohexadiene to give the bicyclic 3,6-dihydro-2//-1,2-ox-azine 3 in 81% yield and d.r. 99 1, The absolute configuration of the reaction product was ascertained unequivocally by synthetic methods as (17 ,45)107. 

Recently, Kibayashi s group (85JA5534) elegantly carried out the stereo-controlled total synthesis of gephyrotoxin (skin extracts of neopropical poison dart frog) based upon an intramolecular nitroso Diels-Alder reaction. The hydroxamic acid 365 was treated with tetrapropylammonium periodate... 

Oxidation of diene-containing hydroxamic acids has been reported to give acylnitroso species which undergo spontaneous hetero-IMDA reactions to give heterobicyclic ketones. (E,E)-N-Hydroxy-5,7-dodecadienamide, upon treatment with tetrapropylammonium periodate, gave the pyrido[l,2-b][l,2]oxazine structure in high yield88. 

C.iii. Nitroso-Type Compounds. Nitroso compounds (R—N=0) show reactivity as dienophiles in Diels-Alder reactions, giving heterocyclic rings. In Kibayashi s synthesis of fasicularin, " for example, hydroxamic acid 180 was treated with tetrapropylammonium periodate in the presence of 9,10-dimethyl-anthracene to give transient acylnitroso compound 181, and the resultant Diels Alder product 182 was formed in 84% yield. In this particular example, the Diels-Alder adduct essentially "protected" the acyl nitroso unit, which was used in a subsequent reaction. 

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