Stereoselective Intramolecular [2+2] Trapping of 1,2-Cyclohexadienes: a Route to Rigid, Angularly Fused Tricyclic
Christian L Jankovic1, Kyle C McIntosh1, Verner A Lofstrand1
1Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2, Canada.
Abstract:
1,2-Cyclohexadienes generated under mild fluoride-mediated desilylative conditions undergo efficient intramolecular [2+2] trapping, providing tricyclic alkylidene cyclobutanes with complete diastereoselectivity for the cis-fused products. Pendent styrenes or electron-deficient olefins can trap simple 1,2-cyclohexadienes or their oxygenated counterparts, with 14 substrates being disclosed. Reactions proceed at ambient temperature using just cesium fluoride in up to 91 % yield, and the necessary precursors are easily accessed from substituted 2-bromocyclohexenones. Multiple synthetic routes have been developed to install the appropriate functional groups required for [2+2] trapping.
Related Concept Videos
Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
Stereoisomerism of Cyclic Compounds
Thermal Electrocyclic Reactions: Stereochemistry
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
Cycloaddition Reactions: Overview
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

![Solid-phase Synthesis of [4.4] Spirocyclic Oximes](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F58508.jpg&w=3840&q=50)
