Various systems for the formation of iodo-azide derivatives of alkenes have been examined. Iodine(I) azide, formed from sodium azide-iodine(I) chloride, has been found to exist in acetonitrile as a complex with sodium azide. The addition of iodine(I) azide to 5α-androst-2-ene in both dichloromethane and acetonitrile has been examined in detail, as well as the addition of thallium(I) azide-iodine in dichloromethane to the same substrate. Products were identified as those arising by diaxial opening of either α- or β-iodonium ions, or by cis-addition to the α-face of the alkene. Addition of iodine(I) azide in dichloromethane to 3-methyl-5α-androst-2-ene gave a cis-adduct as the major product, in addition to trans-diaxial adducts and a trans-diequatorial adduct. Formation of the products was rationalised as arising from c-3 carbocations or from trans-diaxial opening of either α- or β-iodonium ions. The major product from the reaction in acetonitrile was one of ring contraction. No cis product was formed in this reaction but an elimination product was present. Products from the latter reaction were postulated as arising from trans-diequatorial or trans-diaxial opening of either α- or β-iodonium ions. The reaction of sodium azide-iodine-crown ether with 3-methyl-5α-androst-2-ene in chloroform gave a high yield of the same product as those obtained in the reaction with iodine(I) azide in acetonitrile. The reaction of thallium(I) azide-iodine in dichloromethane with the above alkene gave products which could have all arisen via a c-3 carbocation. Solvolysis of the trans-iodo-azides of 5α-androst-2-ene with silver(I) acetate in acetic acid occurred with retention of configuration showing that azide acted as a neighbouring group in the reaction. Solvolysis of the trans-iodo-azide(94) of 3-methyl-5α-androst-2-ene gave, inter alia, a product where azide migration had occurred. Solvolysis of the trans-iodo-azide(95) gave mainly products of elimination. The action of iodine(I) azide on 3-methylene-5α-androstane and 1-mewthylene-4-tert-butylcyclohexane was examined and found to be non-regio- and non-stereo-specific. Iodo-azides were also formed from 3-tert-butylcyclohexene and 3-methoxycyclohexene. In each reaction the major product was that of trans-diaxial opening of the cis-iodonium ion, while the second major product arose by trans-diequatorial opening of the trans-iodonium ion. The ratio of diaxial to diequatorial product varied with the iodo-azide-producing system being used, and was larger in the case of 3-methoxy-cyclohexene, especially when the solvent was dichloromethane. A mechanism was postulated which involves reversible formation of iodonium ions as the fast step followed by rate-limiting attack by azide ions. Solvolysis of these iodo-azides was also investigated. Prior to the current work, both an AdE2 and an Ad3 mechanism had been postulated for the addition of iodine(I) azide to alkenes and in an attempt to distinguish between these possibilities a kinetic study was initiated. Preliminary results indicate that the reaction with cyclohexene is electrophilic and second order.
| Identifer | oai:union.ndltd.org:ADTP/276053 |
| Date | January 1977 |
| Creators | Smith-Palmer, Truis |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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