Unexpected Alkene Isomerization during Iterative Cross-Coupling To Form Hindered, Electron-Deficient Trienes

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Stereoselective Synthesis

Background:

• Conjugated trienes are important synthetic intermediates.
• Bicyclic terpenes require precise stereoselective synthesis.
• Cross-coupling reactions are powerful tools in organic synthesis.

Purpose of the Study:

• To explore an iterative cross-coupling approach for conjugated trienes.
• To achieve stereoselective synthesis of bicyclic terpenes.
• To investigate unexpected alkene isomerization during synthesis.

Main Methods:

• Utilized a bifunctional bromoboronate building block.
• Employed sequential Suzuki coupling reactions.
• Synthesized a conjugated trienone target with a tetrasubstituted alkene.

Main Results:

• Successfully synthesized a conjugated trienone target.
• Observed unexpected alkene isomerization during the final cross-coupling step.
• Determined that ketone conjugation, not steric hindrance, caused isomerization to trans products.

Conclusions:

• The iterative cross-coupling approach is viable for conjugated triene synthesis.
• Alkene isomerization is influenced by electronic effects (ketone conjugation) rather than sterics.
• This finding impacts the stereoselective synthesis of complex molecules like terpenes.