1 research outputs found
Using Ring Strain to Control 4π-Electrocyclization Reactions: Torquoselectivity in Ring Closing of Medium-Ring Dienes and Ring Opening of Bicyclic Cyclobutenes
Syntheses of strained
cyclic dienes were accomplished via palladium(II)-catalyzed
oxidative cyclizations of terminal bis(vinylboronate esters). The
reactions generate strained (<i>E</i>,<i>E</i>)-1,3-dienes that undergo spontaneous 4π-electrocyclizations
to form bicyclic cyclobutenes. Formation of the cyclobutenes is driven
by the strain in the medium-ring (<i>E,E</i>)-1,3-diene
intermediate. Thermal ring openings of the cyclobutenes give (<i>Z</i>,<i>Z</i>)-1,3-diene products, again for thermodynamic
reasons. DFT calculations verified the thermodynamic versus kinetic
control of the reactions, and kinetic studies are in excellent agreement
with the calculated energy changes. An extension of the tandem coupling/4π-electrocyclization
pathway was demonstrated by a palladium(II)-catalyzed oxidative homocoupling/8π-electrocyclization
cascade