Vanadium oxyfluorides

Oxidative coupling of aryl tetrahydroisoquinolines. This reagent is superior to thallium(III) trifluoroacetate or vanadium oxyfluoride for nonphenolic oxidative coupling of substrates such as 2 to provide aporphines and homoaporphines (3). 

Vanadium oxyfluorides also react with hydrogen peroxide to yield complex compounds.2 These are not so well defined as in the case of the peroxyfluorides of niobium and tantalum. 

The norbelladine derivative 408, which served as the starting material for the synthesis of ( )-oxocrinine (415) (Scheme 35), may be readily prepared from the reductive animation of piperonal with tyramine followed by acylation with trifluoroacetic anhydride (191,192). When the N-acylated monophenol 408 was treated with excess thallium tris(trifluoroacetate) in methylene chloride, the di-enone 412 was obtained in 19% yield (191), whereas use of the oxidant vanadium oxyfluoride in trifluoroacetic acid/trifluoroacetic anhydride afforded 412 in 88% yield (192). Base-induced N-deacylation of 412 was accompanied by spontaneous cyclization to furnish racemic oxocrinine (415). Attempts to oxidize the free amine derived from 408 led to the formation of a number of products, some of which resulted from oxidation at nitrogen. 

A particularly interesting and useful synthesis of 130b has been described by Kupchan et al. (141-143), who oxidized the 1-benzyltetrahydroisoquino-line (192, R = COCF3) with vanadium oxyfluoride (Scheme 40). Earlier Kametani et al. (144) had oxidized 192 (R = C02Et) with potassium fer-ricyanide and had obtained 193 (R = C02Et) in 2% yield. 

Morphinandienones have also been synthesized by the oxidation of mono-phenolic benzylisoquinolines with vanadium oxyfluoride in trifluoroacetic acid, other products of the reaction being proaporphines, and similar oxidations have been accomplished with phenethylisoquinolines.183 The same reagent will oxidize the lactam (150) to the dienone (151), which is an analogue of dehydrometatheb-ainone, and the same cyclization may be effected by electrochemical oxidation.184... 

The use of vanadium oxyfluoride as a reagent for the intramolecular oxidation of non-phenolic substrates (158) provided a convenient synthesis pathway to dibenzocyclo-octadienes (Scheme 34). It was shown that the racemic diarylbutane... 

Since the mid-1950s, phenol oxidative coupling (7) has been actively applied to the synthesis of many types of alkaloids, with considerable progress being achieved especially in the field of isoquinoline alkaloids (8-H). As to aporphine synthesis, employment of new reagents such as vanadium oxyfluoride (12) greatly improved yields as compared to classical methods such as oxidation with potassium ferricyanide and ferric chloride. 

As usually prepared, uranium hexafluoride may he contaminated with other volatile fluorides, and hydrogen fluoride, molybdenum hexafluoride, vanadium oxyfluoride are among the common and objectionable impurities that may be present. Purification is usually achieved by distillation procedures and a considerable amount of useful and practical information on purification procedures has recently become available (24, 62, 81). A procedure for the purification of UFe that has been recently introduced by Gathers el al. (16) involves the formation of a complex compound between uranium hexafluoride and an alkali metal fluoride. Ruff and Heinzelmann (68) first observed complex formation between uranium hexafluoride and sodium or potassium fluoride, and this was confirmed by Martin et al. (69). These reports were received with a certain reserve, because efforts made during World War II to prepare addition compounds of uranium hexafluoride were singularly unsuccessful (41). Nevertheless, complex compounds are indeed formed, according to the reaction... 

Another spiro compound has been obtained from the oxazolidine illustrated by the use of essentially the same reagent (ref.78). N-3-trichloroethoxycarbonyl-(2R)-4-hydroxybenzyl-(5S)-3,4-dimethoxyphenyloxazolidineindichloromethane upon treatment with vanadium oxyfluoride in trifluoroacetic/trifluoroacetic anhydride at -78 to-10 C afforded the para-para coupling product. 

Syntheses of 0-methylthalisopavine (59b) have been recorded. In one of these the construction of the carbon-nitrogen skeleton was effected by oxidative cyclization of the lactam (58) to the lactam (59a) by vanadium oxyfluoride in acetonitrile, in 40% yield. Reduction of (59a) by diborane in tetrahydrofuran gave the tertiary amine (59b). An alternative synthesis involved the cyclization, with sulphuric acid, of the acetal (60), prepared from deoxyveratroin. " ... 

Anodic and chemical oxidative coupling of homolaudanbsine (158 R = Me) yields homoglaucine, but oxidation of N-acyl-nor-analogues, e.g. (158 R = COF3), by vanadium oxyfluoride in trifluoroacetic acid and anhydride affords a... 

OXIDATIVE COUPLING Vanadium oxytiifluoride. Vanadium oxyfluoride-Trifluoroacetic acid. 

The tactics employed by Park and coworkers in the synthesis of ( )-sep-ticine (rac-1272) described previously (c Scheme 160) were also used in a related synthesis of ( )-secoantofme (rac-1278) (Scheme 162). In this case, the O-alkylated hydroxamate 1307 bears two different aryl substituents, as required in the target alkaloid. The conversions via intermediates 1308, 1309, and 1310 paralleled those in the synthesis ofsepticine. The final reduction of the pyridone 1310 with lithium aluminum hydride was also successful, leading to rac-1278 in 57% overall yield based on 1307. As in the other examples discussed above, the authors also performed an oxidative coupling of the aryl rings with vanadium oxyfluoride to give ( )-antofme (rac-1275). 

Intramolecular coupling of the related 1,2-diaryI-ethenes (366) to give (367) has been brought about by using vanadium oxyfluoride in TFA and CH2C12,... 

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