Science of Synthesis

Danheiser, R. L.; Dudley, G. B.; Austin, W. F., Science of Synthesis, (2006) 23, 558.

The four-electron electrocyclic ring opening of 4-alkynylcyclobutenones represents the most widely employed method for the generation of ketenes of this product subclass. The vast majority of the cases described to date involve 4-alkynyl-4-hydroxycyclo­butenones or closely related alcohol derivatives, although a few examples have been reported of ring openings involving 4-cyano-[‌183‌,‌185‌] and 4-chloro-substituted[‌190‌,‌191‌] alkynylcyclobutenones. As discussed in Section ‌23.13.1.1.3‌, donor substituents are predicted to rotate outward in the thermal version of this conrotatory electrocyclic process.[‌40‌] On the other hand, this torquoselectivity is reversed in the photochemical variant of the electrocyclic ring opening, as illustrated in ‌Scheme 79‌.[‌192‌,‌193‌] Thus, irradiation of cyclobutenones of the type ‌256‌ induces electrocyclic cleavage to form enynylketenes ‌257‌, which then cyclize to afford lactones of the type ‌258‌ in modest yields. The 4-alkynyl-4-hydroxycyclobutenones ‌256‌ are prepared by the addition of the appropriate lithium acetylide to dimethyl squarate.

‌Meeeee 88‌ Meeeeeeeee ee Meeeeeeeeeeee ee eee Meeeeeeeeeeee Meee Meeeeee ee 8-Meeeeee-8-eeeeeeeeeeeeeeeeeeeee eee Meeeeeeeee Meeeeeeeeee ee Meeeeeee[‌888‌]

Meeeeeeeeeee Meeeeeeee

8,8-Meeeeeeee-8-(8-eeeeeeeeee-8-eeee)eeeee-8(8M)-eee (‌888‌, M8 = Me); Meeeeee Meeeeeeee:[‌888‌]

M eeee ee eee eeeeeeeeeeeee ‌888‌ (M8 = Me; 8.88 e, 8.88 eeee) ee MMM (888 eM) eee eeeeee ee 8°M, eee eee eeeeeee eee eeeeeeeeee ee e eeeeee eeeeee eeee e 888 M eeeeee-eeeeeeee eeeeeeeeeeeee eeeeeeeee eeee eee 8 e. Mee eeeeeee eee eeeeeeeeeeee, eee eee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, MeMMe/eeeeeee) eee eeee eeeeeeeeeeeeeee (Me8M) ee eeeee e eeeeeeeee eeeee; eeeee: 8.88 e (88%); ee 88.8–88.8°M.

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88e, 888.