Silicon-Directed Nazarov Cyclization: Stereochemical, Mechanistic, and Substituent-Compatibility Studies

In the Silicon-Directed Nazarov Cyclization (SDNC) an organosilyl group, attached to a divinyl ketone at a position beta to the carbonyl, directs the location of the double bond in the cyclopentenone ring. Various studies are described that explore the stereochemistry, scope, and mechanism of the reaction. The cyclization proceeds with good to excellent stereoselectivity in cyclohexenyl systems bearing a variety of ring substituents. In all cases the trans family of isomers predominates; cis ring-fused products are formed almost exclusively. The stereoselectivity is high ($>$9:1) with bulky substituents. The potential for improving stereocontrol by increasing the bulk of silicon substituents was explored with 3-methyl-substituted cyclopentenyl-, cyclohexenyl-, and cycloheptenyl-vinyl ketones. Augmenting the bulk of the silyl group enhances the stereoselectivity with five- and six-membered rings. Selectivity is poor in cycloheptenyl systems with a methyl group on the stereogenic center, irrespective of the bulk of the silicon appendage. However, with cycloheptenyl- and cyclooctenyl-substrates bearing a 3-benzyloxymethyl group the products are principally ($>$92%) of the cis stereochemical family. Stereochemical results in the five- and six-ring systems are consistent with a steric approach control model, in which the vinylsilane prefers to attack the least-hindered face of the internal olefin.

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

• Habermas, Karl Louis

Contributors dc:contributor

• Denmark, Scott E.

• Chemistry, Organic

Identifier

(UMI)AAI9411642

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/72291