Remarkably Facile Hexatriene Electrocyclizations as a Route to Functionalized Cyclohexenones via Ring Expansion of Cyclobutenones

Abstract

This Communication describes a cascade reaction sequence that leads to highly functionalized cyclohexenones starting from reaction of cyclobutenones with alpha-lithio-alpha,beta-unsaturated sulfones and amides. The hexatriene-cyclohexadiene cyclization steps presumed to be involved in these transformations are among the most facile hexatriene electrocyclizations reported thus far.

Chemoselective Cyclizations of Divinyl Ketones to Cyclohexenones Mediated by Lewis Acid and Base

“…7 We realized that the key hexatriene intermediates could alternatively be generated by γ-enolization of the readily available divinyl ketones (1) (Scheme 1). Although generation of extended enolates from R, -unsaturated carbonyl compounds was typically accomplished by reactions with strong bases, 8 we believed that enolization of a complex of 1 with a Lewis acid could be achieved under milder conditions using a tertiary amine base.…”

“…13 Cyclization of the camphor-derived enone furnished a single diastereomer of the product (entry 5), whose stereochemistry was consistent with a disrotatory 6π-electrocyclization involving the exo face of the intermediate enolate. 7 The reaction in entry 6 appeared to be more complicated and produced a mixture of two diastereomers in a 78:22 ratio. Apparently, the observed product ratio reflects the thermodynamic stability of the two diastereomers, as a sample of pure trans-15 gives rise to the same ratio of isomers upon standing in chloroform for 3 days at room temperature (Scheme 3).…”

Synthetic Studies toward Bi-linderone Lead To Unexpected 6π-Electrocyclization Reactions: A Facile Construction of Highly Congested Spiro Compounds

“…For instance, Spangle and co-workers disclosed that alkyl substituents on either C1 or C3 position could accelerate the cyclization. 10 Sulfonyl substitutions were confirmed as an accelerating factor by Magomedov 11 and Brangänge and respective co-workers. 12 Marvel and coworkers reported that ester groups on C2 and C5 facilitated the cyclization.…”

A solvent-free, base-catalyzed domino reaction towards trifluoromethylated benzenes from bio-based methyl coumalate

“…Moreover, the present case of 6π-ERC might be facilitated by a push/pull type mechanism, between the hydrogen bonded enol and the proximal carbonyl (RCO). 27 ChemDraw® calculation of CF 3 -triene intermediate D, applying the extended Hückel method, suggested both large partial positive and negative charges at C-1 and C-6. Carba-6π-electrocyclic ring closure would therefore be favored.…”