Iodo azides from alkenes

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... 

Iodine azide, generally made in situ from ICl and NaNa in MeCN at 0 C, adds readily to alkenes by a similar heterolytic mechanism to INCO. Whereas the trans stereochemistry is generally well established,the regiochemistry of the adduct with 1-phenylcyclohexene has been queried recently it was originally formulated as the l-azido-2-iodo compound (Scheme 86), but base treatment was subsequently shown to yield what appeared to be 6-azido-l-phenylcyclohexene, which would have arisen from the l-iodo-2-azido isomer. However, it has very recently teen shown by 3(X) MHz NMR that the elimination product is in fact 3-azido-l-phenylcyclohexene, derived ultimately (Scheme 86) from the originally proposed l-azido-2-iodo- structure. 

The dipolar cycloaddition of an alkyl azide with an alkene to form an aziridine has been exploited in the total synthesis of the alkaloid ( )-aspidospermidine <20050BC213>. Enone 353 was prepared in 11 steps from 3-ethoxycyclohexenone and coupled to 2-iodo nitrobenzene under Ullman cross-coupling conditions. The acetate group of 354 was hydrolyzed and the resulting alcohol converted to an azide using standard conditions in 75% overall yield. The cycloaddition of the azide with the enone was conducted in refluxing benzene for 3 days. The fused-ring aziridine 355 was the only product isolated. None of the initial dipolar cycloadduct triazoline was observed. The... 

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