Hydrazones reaction with iodine

Vinyl iodides1 or selenides.2 Some time ago Barton and Stemhall reported the conversion of ketone hydrazones to a mixture of vinyl iodides and gem-diiodides by reaction with iodine in the presence of triethylamine (4, 260). Formation of vinyl iodides is significantly enhanced if a strongly basic pentaalkylguanidine (11, 249-250) is used in place of triethylamine. Formation of diiodides is also suppressed by addition of the hydrazone to a solution of the base and an electrophile. 

Table 1. Reaction of Hydrazoiies and Hydrazone Derivatives with Iodine Monofluoride...

As noted above, it is not easy to purify unsubstituted hydrazones. Therefore, reactions of hydrazone derivatives with iodine monofluoride have also been studied (Table 1). A-Methyl-and iV,iV-dimcthylhydrazones react more slowly than unsubstituted hydrazones with iodine monofluoride higher tempteratures are often required for their conversion into ge/w-difluorides (Table 1). The reason for this behavior is that elimination of iodomethane from the intermediates is less favorable (see Scheme 1, R = Me). The use of pure derivatives increases the yield in cases sensitive to hydrolysis (cf. entries 25 and 26). 2,4-Dinitrophenylhydrazones only react with iodine monofluoride at temperatures above O C. The yields are generally lower than in the case of unsubslituted hydrazones, and 2,4-dinitrophenylhydrazones formed from aldehydes are unreaetive. 

As already noted, azines are unreactive towards iodine monofluoride however, it has been shown that azines react with bromine trifluoride under mild reaction conditions, yielding gem-difluorides (Table 2).4 The reagent bromine trifluoride is readily prepared from its elements, although caution should be taken because bromine trifluoride reacts violently with water and acetone. 2,4-Dinitrophcnylhydrazones can a Iso be used as the hydrazone dcri va ti ves i n reactions with bromine trifluoride (Table 2). No significant byproducts, unlike the reactions with iodine monofluoride, are obtained in this case. The reactions with bromine trifluoride are not sensitive to the stereochemistry of the C = N bond, and both E- and Z-isomers react with the same efficiency. 

Reaction of hydrazones with iodine under basic conditions, to give azines, shows evidence of diazo intermediates that can be trapped with an internal alkene or alkyne function.92... 

Vinyl iodides. The reaction of iodine in the presence of triethylamine with ketone hydrazones can result in gem-diiodides or vinyl iodides (4, 260). Hindered hydrazones are converted mainly into the latter products however, yields are generally only moderate. 

The reaction of hydrazones and their derivatives 1 with iodine monofluoride (IF), prepared from the elements, yields the corresponding gem-difluoro compounds 2 (Table 1). Unsubstituted hydrazones 1 (R = R = H) are usually the most suitable substrates for this transformation. 

Semicarbazones (Table 1, R = CONH2) also react with iodine monofluoride. The gem-difluoro compounds are generally obtained in lower yields than with unsubstituted hydrazones, but the corresponding aldehyde derivatives (entry 16) arc reactive in this case. Finally, in the reaction of tosylhydrazones, gew-difluorides are obtained in only low to moderate yields (entries 4 and 23). 

For experimental procedures for fluorinations with iodine monofluoridc and bromine trifluoride, sec the reactions of hydrazones (Section 1.1.9.1.). 

Hydrazones can be converted into gc/n-difluorides upon reaction with either fluorine [245], bromine monofluoride (generated in situ) [246] or iodine monofluoride [247], and the reaction of diazoketones with fluorine results in similar transformations [248] (Figure 3.50). 

The basic triethylamine promotes an ionic reaction leading to the diazo compound (32), which then reacts with iodine in tetrahydrofuran probably through the iodonium compound (23) to give the iodo-product (24. Steroidal 17- and 20-hydrazones give the vinyl iodides (25) and (26) respectively. 

This type of compound was prepared from aldehydes 216 by conversion into the bis(arylhydrazone) 225, which, upon reaction with copper sulfate, afforded the corresponding triazoles 227 (Scheme 48). When 216 was allowed to react with amines or hydrazines having substituents that differ from that in 216, the corresponding mixed bis(hydrazones) 228-230 were prepared. Attempted oxidation of bis(benzoylhydrazone) 231 with iodine and mercuric oxide to give 232 was investigated (80MI7). 

Preparation. This iodide can be prepared in 60% yield by the reaction of ethylidene chloride (Aldrich) with ethyl iodide and aluminum chloride. It can also be prepared by the reaction of acetaldehyde hydrazone with iodine and triethylamine (4, 260). This method is based on the procedure of Pross and Sternhell. ... 

When the substrates were hydrazone derivatives of alkyl cyclopropyl ketones, (alk-1 -enyl)cyclo-propanes were obtained by treatment with chlorotrimethylsilane and iodine in the presence of triethylamine. In the latter type of reactions, iodine incorporation occurs in one of the steps, giving 1-cyclopropyl-l-iodoalk-l-enes. 

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