Orbital control and selectivity in addition reactions [article]

Dugald Quentin McDonald, University Of Canterbury
2013
Several topics which are relevant to the results and methods in this thesis are examined in Part I. Recent developments in the application of molecular orbital theory to the Diels-Alder reaction and the history and development of semi-empirical molecular orbital methods are reviewed. A survey of the major developments in understanding diastereofacial selection in the Diels-Alder reaction is also included in Part I. In Part II experimental and molecular mechanics studies are described for the
more » ... ition of several azo, acetylenic and alkene dienophiles with four cage-fused dienes. Reactions of a dihydroxy substituted cage diene were found to proceed with complete selectivity for reaction from the face of the diene anti to the cyclobutane group, with the exception of the reaction of nitrosobenzene which was determined to be reversible. For most of the dienophiles, however, molecular mechanics calculations of the products in the reactions confirm that the relative stability of the adducts does not control the diastereofacial selection in the reaction. With a series of mono- and dimethylidene substituted cage-fused dienes, reactions of alkene dienophiles showed a strong preference for reaction from the anti face of the diene and this is successfully rationalized by a transition state model based on molecular mechanics. A series of mono and dimethylidene substituted cage dienes showed an opposing trend in facial selectivity, upon reaction with acetylenic dienophiles, to that observed with azo dienophiles. The selectivity observed for the reactions of acetylenic dienophiles cannot be rationalised by the "steric only" molecular mechanics based transition state models and this is interpreted as pointing to the importance of direct interactions between the substituents on the cage diene and the approaching dienophile. Several studies on the chemistry of cage-fused dienes are described with emphasis on the importance of transannular interaction during attempts to effect functional group interconversions of the cage substitue [...]
doi:10.26021/8407 fatcat:kevtevd7czap7pvabdnlwrpqee