Silicon-Directed Nazarov Cyclization

A new variation of the Nazarov cyclization has been developed in which an organosilyl group beta to a divinyl ketone directs the incipient double bond to the thermodynamically less stable position. Two general methods for preparing beta-silyl divinyl ketones are reported. Ferric chloride induces cyclization under mild conditions in good yields with predictable and complete control over the position of the double bond. An extensive study of the scope, mechanism, and stereochemical outcome of the reaction is also reported. This variant of the Nazarov cyclization is quite general for the preparation or annelation of cyclopentenones. The observed effects of substituents on reaction rate can be explained by a rate-limiting cationic electrocyclization. The degree of stereochemical control was modest (ca. 3:1) in forming the indenone ring system. The substituent in the major isomer was always cis to the ring fusion protons. Thorough spectroscopic and conformational analysis revealed that divergent senses of electrocyclization were responsible for the observed products. Additional experiments suggest that steric, rather stereoelectronic forces control the sense of cyclization. A qualitative description of the nature of reactive intermediates in the silicon-directed Nazarov reaction is proposed as well as an explanation for the remarkable efficacy of ferric chloride for inducing the reaction. Silyl substitution has been shown to retard the reaction.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Jones, Todd Kevin

• Chemistry, Organic

Identifier

(UMI)AAI8511622

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70291