Files in this item
|(no description provided)|
|Title:||Intramolecular Heterodiene (4+2) Cycloadditions of Nitrosoalkenes, Nitroalkenes, and Vinyl Nitrosonium Ions|
|Author(s):||Dappen, Michael Scott|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Intramolecular 4+2 cycloadditions with three related heterodienes: nitrosoalkenes, vinyl nitrosonium ions, and nitroalkenes are discussed. An appraisal was made for each diene in terms of the ease of generation of the heterodiene, the ability to undergo facile cycloaddition, and the facility for further elaboration of the cycloadduct.
A study of the ability of (alpha)-chloro ketoximes and silyloximes to serve as precursors for nitrosoalkenes showed that (alpha)-chloro ketoximes produced nitrosoalkenes efficiently regardless of oxime geometry or disposition of the chlorine atom. (alpha)-Chloro silyloximes were less efficient in production of nitrosoalkenes. Application of this to precursors for the formation of 6-6 ring systems led to excellent yields of 4+2 cycloadducts. The use of (alpha)-chloro silyl oximes and anhydrous fluoride metal salts gave hydronaphthalene rings systems in greater than 80% yield. Extension to 6-5 ring systems lowered the yield and stereoselectivity of the reaction.
(alpha),(beta) Epoxy ketonitrones were shown to be poor precursors of vinyl nitrosonium ions. Proton and carbon VI NMR studies indicated that treatment of these nitrones with trimethylsilyl trifluoromethanesulfonate generated the reactive species very slowly at room temperature. Preparative scale reactions gave poor to moderate yields of cycloadducts. A dependence on nitrone geometry was noted, Z-(alpha),(beta) epoxy ketonitrones were required for the reaction but unavailable since the E nitrone is favored thermodynamically in their preparation.
Cycloadditions with alicyclic nitroalkenes under Lewis acid catalysis were shown to be facile. The cyclic nitronic esters that result from these reactions can be rearranged to hydroximic lactones and subsequently hydrolyzed to lactones. They were also shown to act as dipolarophiles in a very efficient 3+2 cycloadditions.
Finally, an unusual stereoelectronic effect was shown to be governing the conformation of certain (alpha)-chloro oximes and silyloximes, forcing 2,3-trans substituents on a cyclohexyl ring to be diaxial. This phenomenon has been termed the vinylogous anomeric effect since its origin can be seen as the n-(sigma)* interaction of the oxime oxygen lone pair electron transmitted through the (pi)*(,C=N).(, )
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.
|Date Available in IDEALS:||2014-12-15|