Oxime ethers hydroxylamine synthesis

Strategies that lead to the formation of isoxazoles during cleavage from an insoluble support include the oxidative cleavage of /V-(4-alkoxybenzyl)isoxazolidincs with DDQ to yield isoxazolines (Entry 14, Table 15.16), the nucleophilic cleavage of 2-acyl enamines with hydroxylamine (Entry 15, Table 15.16), and the acidolysis of 2-cyano-phenols etherified with an oxime resin (Entry 17, Table 15.16). The required oxime ethers for the latter synthesis were prepared by reaction of the corresponding 2-fluorobenzonitriles with Kaiser oxime resin [203],... 

Benzofurans and Other Annelated Furans.-A new synthesis of benzofurans (73) is by the reaction of the phosphonium salt (72) with acid chlorides RCOCl in the presence of triethylamine. The benzofuran (74) results from the condensation of hexafluorobenzene with acetylacetone. Three instances of the formation of benzofurans from O-aryl-hydroxylamines, i.e. the oxygen analogue of the Fischer indole synthesis, have been reported O-phenylhydroxylamine hydrochloride and benzenesulphonylacetone give a 2 1 mixture of compounds (73 R = CH2S02Ph) and (75), the oxime ether (76) is converted into the aldehyde (77 ... 

Enmein was converted to 20-hydroxykaur-6-en-15a-pyranylether (382), which was oxidized with chromium trioxide in pyridine to afford the aldehyde 383. The latter was converted with hydroxylamine to the oxime 384. The nitrone 385 was prepared by treatment of 384 with bromine azide. Photolysis of 385 gave the desired compound 381 in 46% yield. This intermediate possesses several useful functionalities (e.g., carbinolamine ether linkage), which may be of interest for synthesis of C20-diterpenoid alkaloids after minor changes in this scheme. 

The readily available 2,3,4,6-fefra-O-benzyl-D-glucopyranose (11) can be used for the synthesis of both nojirimycin (1) and 1-deoxynojirimycin (2) (Schemed).It was treated with EtSH to furnish 12, which was oxidized to the corresponding ketone 13 using TPAP, while the Swern oxidation method failed to produce 13. Treatment of 13 with mercury(ll) salts in the presence of methanol followed by treatment with hydroxylamine hydrochloride in the presence of pyridine afforded the oxime 14 in 73% yield. Treatment of 14 with LiAlH4 in diethyl ether followed by N-protection of the resulting diastereomeric mixture of amines with di-rert-butyl dicarbonate furnished 15 and 16 in 65 and 15% yield, respectively. Pearlman s catalytic hydrogenation of 15 over palladium hydroxide in ethanol followed by treatment of the resulting tetrol with SO2 in water furnished the sulfonic acid 17 in 80% yield. Conversion of 17 into 1 was accomplished by treatment with Dowex 1X2 (OH ) resin. 

A variety of different routes to cyclobutane systems involving non-photochemical means has also been devised. Acid catalyzed rearrangement of fused cyclopropyl ether (61) by Wenkert et al. (97, 98) afforded the bicyclic dione (62), which through a thioketal-desulfurization process and treatment with hydroxylamine yielded oxime (58) (Scheme 12). The shortest synthesis of grandisol is that reported by Billups et al. (Scheme 13) (99). Dimerization of isoprene in the presence of a zero-valent bis-cyclooctadienyl-nickel-phosphite complex gave the cis-cyclobutane diolefin (65), which could be separated in 12—15% yield from the complex product mixture by low-temperature distillation. Selective hydroboration and oxidation afforded grandisol. 

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