Stereoselective Preparation of 4,5-Dihydroxy-5,6-dihydro-4H-1,2-oxazines and Their Derivatives
摘要:
cis-Dihydroxylation of 6H-1,2-oxazines 1 proceeds efficiently either by potassium permanganate at low temperature (Method A) or by ruthenium trichloride/sodium periodate at 0-5 degrees C (Method B). The resulting 4,5-dihydroxylated 1,2-oxazines 2 were usually obtained as diastereomerically pure compounds with the two newly introduced hydroxy groups positioned trans to the 6-alkoxy group. These products can be protected by standard methods either as acetals 4 or as diacetoxy compounds 5. In addition, the bicyclic orthoesters 7 and 8, dimesylates 15, and cyclic sulfates 19 have been prepared. First experiments dealing with transformations of the oxygen functionalities are described.