NOVEL RING TRANSFORMATIONS FOR 5,5A-DIBROMOBICYCLOMYCIN AND DERIVATIVES

Both 5,5a-dibromobicyclomycin (2) and 5,5a-dibromabicyclomycin-2',3'-a cetonide (3) were observed to undergo unique ring fragmentation proces ses under basic conditions. Treatment of 2 and 3 with DBU gave (3S. 4S , utoxy-3-ene)-4-hydrox)-5-hydroxymethyl-5-methyl-3- oxamido-gamma-lac tone (4) and (l'S, y-2,3-O,O-isopropylidene-2-methyl-2,3-dioxapropyl) (5) in moderate yields. Dissolution of 3 with KF and 18-crown-6 in DMF yielded 3 and (1S, 5R, I'S, dioxapropyl)-2-oxabicyclo[3.3.2]decan-6,7 ,9-trione (6). The facility of these ring cleavage transformations has been attributed to the favorable stereoelectronic arrangement of the C(6) hydroxy and C(5a) bromo groups in 2 and 3 for elimination.