Regiochemical and stereochemical studies of cationic pi-cyclizations.
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| Format: | Thesis Book |
| Language: | English |
| Published: |
1982.
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| Online Access: | Link to ProQuest Copy Link to OAKTrust copy ProQuest, Abstract |
| Abstract: | Cationic (pi)-cyclization of allenyl alcohols 10a,b and allenyl ketones 11a,b provided evidence that the mode of ring closure of (gamma)-allenyl cationic systems is strongly dependent on the substitution pattern of the allene. Cationic (pi)-cyclization of unsubstituted (gamma)-allenyl systems (11a and 12a) gave only decalin-type products resulting from reaction at the terminal carbon of the allene. The substituted (gamma)-allenyl systems (11b and 12b) gave only hydrindane-type products resulting from reaction at the central carbon of the allene. A general rationale for the regioselectivity of these cyclizations results observed with (gamma)-allenyl systems is developed based upon consideration of orbital overlap as determined from molecular models, and of the effect of alkyl substituents on electrophilic addition to allenes. Cationic (pi)-cyclization of several related cyclohexenyl (53, 54, 56, 57, 58, 59, and 60) and cyclopentenyl (61, 62, 63, and 65) systems provided evidence on the most favored transition state for these stereoselective spirocyclic ring closures. The stereoselectivity induced by cyclohexenyl systems is greater than that of cyclopentenyl systems. Addition of a methyl grop adjacent to the forming spirocyclic center reduces stereoselectivity. Addition of a methyl group to the double bond to form a (delta)-E-olefin increases stereoselectivity in allylic alcohol initiated cyclizations. Addition of a methyl adjacent to the forming spirocyclic center when it is incorporated on a (delta)-E-olefin changes the regioselectivity of the reaction in the case of allylic alcohol initiated cyclizations (but leads to complex mixtures in enone initiated cyclizations). |
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| Item Description: | "Major subject: Chemistry." Typescript (photocopy). Vita. |
| Physical Description: | xi, 104 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 100-103). |