Acetals mass spectral fragmentation

Coupling of the diazotetrazole with ethyl cyanoacetate gave 1034. Its cyclization in boiling acetic acid or pyridine afforded 1035 as the major product in addition to 1036. Mass spectral fragmentation of 1035 confirmed that the azole ring is more stable than the 1,2,4-triazine ring on electron impact [76JCS(P1) 1496] (Scheme 194). 

Mass spectral fragmentation of the products of electron-impact fragmentation of 6-nitro-2,l-benzisoxazole (6-nitroanthranil) [1351], 3-substituted 6-nitroanthranils [1352], 4-arylamino-5,7-dinitrobenzofurazan [747], 4-(2-aminoethylamino)-7-ni-trobenzofurazan [1353], 12-O-tetradecanoyl phorbol-13-O-acetate containing 4-nitrobenzofurazan [1354], and fluorescent probes on the base nitrobenzofurazans [777] have been discussed. 

Several 21,22-seco-diacids (150) have been prepared in the 20/S,28-epoxy-18a,19/8H-ursane series by oxidation of the corresponding 22-hydroxymethylene-21-ketones (151). Reaction of the 21-ketone (152) with oxygen in an alkaline medium afforded the a-hydroxy-acid (153) and the seco-diacid (150). ° Several interesting reactions were observed during this work. ° While pyrolysis of the a-acetoxy-acid (154) yielded the ketone (155) pyrolysis of the seco-diacid anhydride resulted in loss of carbon monoxide and formation of the lactone (156). Lead tetra-acetate oxidation of the ketone (155) [or the hydroxy-acid (153)] followed a Baeyer-Villiger pathway to the lactone (156). The ketone (155) was very susceptible to reduction in the presence of alcoholic alkali. The mass spectral fragmentation of a series of compounds based on 20/8,28-epoxy-18a,19/8H-ursane has been examined. ... 

In contrast with brevianamide A, brevianamide E gave one mole of proline cleanly on acid hydrolysis. Zinc-acetic acid reduction produced a degradation product (28), characterised as an indole an important mass spectral fragment ion at mje 198 corresponds to cleavage as shown. 

Benzyl 2,3,4-triacetamido-2,3,4,6-tetradeoxy-a-D-galacto-pyranoside has been synthesized from the corresponding 3,4,6-tri-O-mesyl-allopyranoside by selective reduction at C-6 (NaBH j-DMSO), followed by azide-displacement of the sulphonates at 3 and 4 with Inversion mass spectral fragmentation of its derived alditol acetate was also recorded. 

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