Electrocyclic Ring Opening of Charged cis-Bicyclo[3.2.0]heptadiene and Heterocyclic Derivatives. The Anti-Woodward−Hoffmann Quest (II)

• Published in: Journal of organic chemistry Vol. 74; no. 6; pp. 2396 - 2402
• Main Authors: Silva López, Carlos, Faza, Olalla Nieto, de Lera, Ángel R.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 20.03.2009
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with n hetero atom and also o and/or s, se, te hetero atoms; Kinetics and mechanisms; Organic chemistry; Preparations and properties; Reactivity and mechanisms; Substituent effect; Electrocyclic reaction; Molecular structure; Nitrogen heterocycle; Isomerization; Woodward Hoffmann rule; Push pull compound; Dienic compound; Ring cleavage; Transition state; Bicyclic compound; Reaction mechanism; Ethylenic compound
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo802678d

The ring opening reactions of fused cyclobutenes have been the subject of mechanistic debate for decades. Some reports have been published recently suggesting that, in some heterocyclic derivatives, the disrotatory anti-Woodward−Hoffmann mechanism might be responsible for the ring opening. We hereby show that the conrotatory pathway is still the lowest energy alternative for all cases examined, including push−pull substituted 2-thia-4-azabicyclo[3.2.0]hepta-3,6-dienes. Actually, we found that the disrotatory transition state exchanges roles with a double-bond isomerization depending on the substituents around the bicyclic structure.