Science of Synthesis

Gaspar, B.; Trauner, D., Science of Synthesis: Stereoselective Synthesis, (2011) 3, 383.

The thermal electrocyclic ring opening of substituted derivatives of cyclobutene (strain energy 28.5 kcal · mol−1) was initially observed to lead to formation of mixtures of two isomeric dienes, which significantly reduced the synthetic potential of this strategy. However, the stereochemical outcome of the process is determined by the electronic properties of the allylic substituents.[‌4‌] In general, π-donor substituents tend to undergo outward conrotation, whereas π-acceptor substituents favor inward conrotation. For example, the aldehyde ‌2‌, generated by the Swern oxidation of alcohol ‌1‌, is crucial for the selective formation of Z,E-dienal ‌3‌ (‌Scheme 1‌).[‌5‌,‌6‌] Importantly, the isomeric E,E-dienal ‌4‌ is accessible from ‌3‌ in excellent yield by acid-catalyzed isomerization to the thermodynamically more stable product.

‌Meeeee 8‌ Meeeeeeee Meeeeeeee ee e M,M-Meeeee ee Meeeeeeeeee Meee Meeeeee eee ee M,M-Meeeee ee Meeeeeeeeeeee[‌8‌,‌8‌]

Meeeeeeeeeeeeeee eeeeeee eeeeee eee eeee ee eeeeeeee eeee eeeee-eeeeeeeeeee eeeeeeeeeeee (‌Meeeee 8‌).[‌8‌] Meeeeeeeee eeee eeeeeeeeeee eeeeeee, eeeee eeeeeee eeee eeeeee eeeee eeeeeee eeeeeeee,[‌8‌] eee M,M-eeeee ‌8‌ ee eeeeeeee ee 88% eeeee eeee eee eeeeeeeeeeeee eeee eeeeeee ee eee eeeeeeeeeee ‌8‌, eeeee ee eeeeeeee ee eee eeeeeeeeee ee eeeeee ‌8‌.

‌Meeeee 8‌ Meeeeeeee ee e M,M-Meeeeee Meee ee Meeeeeeeeee Meee Meeeeee[‌8‌]

Meeee eeeeeeeeeeee, eeeeeeeeeeeeee eee eeeeeeeeeeee eeeeeeeeee eeeeeeeeeeeee eee ee eeeee eeeeee eeeeeeeeee.[‌8‌] Meee eeeeeeeeeee, eeeeeeeeeeeeee eeeeeee eeeeeeeeeee eeeeeeeeeeeee eeee eeeeeee ee eeee eeeeee eeeeeeee e-eeeeeeeeeeeeeee, eeeee eee eeeeeeeee eee eeeeeeee ee ee eeeeeeee, eee eeeee ee eeeeeeee eeeeeeee eeeeeeeeeeeee eee eeeeeee eeeeeeeee.[‌88‌] Me eeeeeeeeeee ee eee eeeee eeeeeeeee ee eeeeeee ee Meeeeeee, e-eeeeeeeeeeeeee ‌8‌, eeeeeeeee ee eeeeeeeeeee ee eeeeeeeeeeeee ‌8‌, eeeeeeeee ee eeeeeeeeeeeeee Meeee–Meeee eeeeeeee ee eeeeee M-eeeeee-M-eeeeeeeeeee (‌88‌) ee e eeeee- eee eeeeeeeeeeeeeee eeeeee (‌Meeeee 8‌).[‌88‌]

‌Meeeee 8‌ Meeeeeeeee ee e Meeeeeee e-Meeeeeeeeeeeee eeee e Meeeeeeeeeeee[‌88‌]

Meeeeeeeeeee Meeeeeeee

(8M,8M)-8-(eeee-Meeeeeeeeeeeeeeeeee)eeeee-8,8-eeeeeee Meee (‌8‌):[‌8‌]

Meeee MeMM (8.88 e, 88.88 eeee) eee eeeee ee e eeee ee eeeeeeee ‌8‌ (8.8 e, 8.88 eeee) ee MMM (88 eM) eee M8M (88 eM). Mee eeeeeee eee eeeeeee ee ee eee 88 e, eee eee eeeeeee eee eeeeeee eeeee eeeeeee eeeeeeee. Mee eeeeeee eeeee eee eeeeeeeee eeee MeMM ee eM 8 eee eeeeeeeee eeee MeMMe. Mee eeeeeeee eeeeeeee eeee eeeeee eeee eeeee, eeeee (MeMM8), eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeeeeeeeeeeeeee (MeMM) ee eeee eeeeeeee ‌8‌ ee eeeeeeeee eeeeeeee; eeeee: 8.88 e (88%); ee 888–888 °M.

M-Meeeee-M-eeeeeeeeeee (‌88‌):[‌88‌]

M eeee ee ‌8‌ (88 ee) ee 8,8-eeeeeeeeeeeeeee (8 eM) eee eeeeeee eeeee ee eeeeeeeeee ee M8 eee 8 e ee 888 °M. Meeee eeeeeeeeeee ee eee eeeeeee, eee eeeeeee eee eeeeeeeeeeeeee (MeMMe) ee eeee M-eeeeee-M-eeeeeeeeeee (‌88‌) ee eeeeeeeee eeeeee; eeeee: 88.8 ee (88.8%); ee 888–888 °M.

References