Preparation of Vicinal Azidohydrins by Reaction of Oxiranes with Triethylaluminium/Hydrogen Azide

A novel, mild, and highly stereoselective transformation of epoxides to azidohydrins by treatment with Et₃Al/HN₃ in toluene is described. As an example for the versatility of the reaction, a polyfunctional compound, 14,15-epoxy-14,15-dihydromilbemycin D ( 1 ), was transformed to 14-azido-14,15-dihydro-15-hydroxymilbemycin D ( 2 ) in 61% yield.     

Synthesis and Configuration of Some Hydroxymilbemycin Derivatives Including 22,23-Dihydroavermectin B1b Aglycone

The synthesis of several configurationally defined hydroxymilbemycin derivatives is described. One of these allylic alcohols is the known 5-O-[(tert-butyl)dimethylsilyl]-13α-hydroxymilbemycin D (= 5-O-[(tert-butyl)-dimethylsilyl]-22,23-dihydroavermectin B _1b, aglycone; 15D ), the synthesis of which represents LI conversion of the milbemycin to the avermectin series of natural products. The configurations at C(13), C(14), and C(15) of the new milbemycin derivatives were determined by NMR experiments and force-field calculations.     

Photochemical reactions, 135th communication Photochemistry of Homoconjugated Cyclobutanones. II. Decisive Effect of gem- Dimethyl Substitution on the Course of the Oxa-di-π-methane Rearrangement

The synthesis and photolysis of the spirocyclobutanones 4–7 incorporating a cyclohexa-, cyclohepta- and cyclooctadiene moiety, respectively, is described. On triplet excitation, these compounds undergo isomerization via a 1,2-acyl shift involving one or both double bonds of the diene system. The presence of a gem-dimethyl group as in 1 , 4 and 7 dramatically changes the photoproduct distribution, since only these substrates leads to the products 3, 29 and 34 resulting from vinylogous ring closure (Scheme 5). Those substrates without methyl substitution ( 5 and 6 ) give only products of a rearrangement involving one double bond.