Iodine azide, electrophilic additions

Iodine azide, on the other hand, forms pure adducts with A -, A - and A -steroids by a mechanism analogous to that proposed for iodine isocyanate additions. Reduction of such adducts can lead to aziridines. However, most reducing agents effect elimination of the elements of iodine azide from the /mwj -diaxial adducts of the A - and A -olefins rather than reduction of the azide function to the iodo amine. Thus, this sequence appears to be of little value for the synthesis of A-, B- or C-ring aziridines. It is worthy to note that based on experience with nonsteroidal systems the application of electrophilic reducing agents such as diborane or lithium aluminum hydride-aluminum chloride may yet prove effective for the desired reduction. Lithium aluminum hydride accomplishes aziridine formation from the A -adducts, Le., 16 -azido-17a-iodoandrostanes (97) in a one-step reaction. The scope of this addition has been considerably enhanced by the recent... 

In the case of electrophilic addition, the reactions of tricyclic dienes 1 with several electrophilic reagents have been investigated.1 7 Interestingly, some of these compounds undergo addition reactions with remarkable syn stereoselectivity. For example, the reaction of dimethyl tricy-clo[4.2.2.02,5]deca-3,9-diene-7,8-dicarboxylate with iodine azide solution, prepared in situ from an excess of sodium azide and iodine monochloride, in acetonitrile at — 5 C provided the. yyn-4-azido-3-iodo derivative 2 (Table 1) in 90% yield.1,2,4,6 The formation of the 5,>,n-4-azido-3-iodo derivative 2 is thought to be the first example of a syn addition of iodine azide to an alkene.1,2 The formation of the syn-product is best explained by the twist strain theory,8 according to which the syn transition structure A is favored over the an/7-coplanar transition structure B.1... 

Alternatively, the addition of iodine azide under similar conditions to 9,10-dimethyltricy-clo[4.2.2.02,5]deca-3,7-diene produced the tetracyclic tetrazole 3, whose formation possibly involves initial reaction of the solvent acetonitrile with the azide ion.1 The addition proceeds via electrophilic attack of iodine azide with the formation of a three-membered iodonium ion intermediate backside opening of the intermediate results in the anti configuration of the tetrazole derivative (see Table 1). 

The addition of iodine azide to double bonds gives p-iodo azides. The reagent can be prepared in situ from KI—NaNa in the presence of Oxone -wet alumina. The addition is stereospecific and anti, suggesting that the mechanism involves a cyclic iodonium ion intermediate. The reaction has been performed on many double-bond compounds, including allenes and a,p-unsaturated ketones. Similar reactions can be performed with BrNa and CfNa. 1,4-Addition has been found with acyclic conjugated dienes. In the case of BrNa, both electrophilic and free-radical mechanisms are important, whUe with CIN3 the addi-... 

Just as bromine chloride is a more reactive electrophile than iodine chloride so one would expect bromine azide acting as an electrophile to be more reactive than iodine azide. In fact in solvents suitable for heterolytic reaction, bromine azide adds to chalcone less readily than iodine azide ° and this further indicates an Adj mechanism. The evidence is strengthened by the occurrence of acid catalysis of the bromine azide addition. 

However, the formation of other compounds of the halogens with other elements in which the sharing of electrons leads to more positive oxidation states for the halogen has served organic chemistry well. Examples of such compounds with positive oxidation states for the halogens were provided in Chapter 6 (cf. Table 6.1), and they include hypochlorous acid (HOCl) nitrosyl chloride (NOCl), iodine azide (IN3), and iodine isocyanate (INCO). It may be recalled that it was argued there that the electron-rich double bond attacked the electrophilic halogen to lead the process of electrophilic addition. 

Two groups have investigated the details of the stereochemistry and mechanism for electrophilic additions to the cyclobutene double bond in the tricyclo[4,2,2,0 ]deca-3,7-diene (875) and its derivatives. With iodine azide, for example, a reagent which normally leads to trans-adducts by an anti-coplanar addition mechanism, addition to (875) occurs only by syn-attack at the sterically unhindered side of the cyclobutene double bond> " a result explained in terms of twist-strain... 

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