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DOI: 10.1055/sos-SD-023-00504

Danheiser, R. L.; Dudley, G. B.; Austin, W. F.Science of Synthesis, (200623559.

4-Alkynyl-4-hydroxycyclobutenones 259 (Scheme 80) are easily obtained by the addition of lithium acetylides to cyclobutene-1,2-diones. As discussed in Section, a variety of cyclobutenediones can be synthesized beginning with squaric acid, and the addition of organolithium compounds proceeds with high regioselectivity provided that the C3 and C4 substituents differ significantly in their electron-donating properties. In 1985 it was shown that the thermolysis of cyclobutenones of type 259 produces benzo-1,4-quinones 263 and 2-alkylidenecyclopentene-1,3-diones 264 via a novel rearrangement (the Moore cyclization). This reaction proceeds via the intermediacy of enynylketenes 260.[‌194‌] In the case of the parent system (R1=R2=R3=R4=H), calculations at the B3LYP/631G(d) level indicate that the cyclization of an enynylketene 260 to form a biradical 261 containing a benzene nucleus is considerably more favorable (ΔG298=13.6 ­kcal·mol1) as compared to cyclization to a biradical 262 based on a methylidenecyclopentadiene ring system (ΔG298=41.4 kcal·mol1).[‌195‌] In the case of more-highly functionalized systems, however, cyclizations to the six-membered product 261 or to the five-membered ring 262 have comparable activation barriers. For the parent system, the biradical 261 (R1=R2=R3=R4=H) has a considerably lower energy (13 kcal·mol1) than the corresponding alternative zwitterionic species.

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Meeeee 88 Meeeeeeee ee Meeee-8,8-eeeeeeee eee eee Meeee Meeeeeeeeeeee ee 8-Meeeeeeeeeeeeeeeeeeee[‌888‌,‌888‌,‌888‌‌888‌]

Meeeeeeeeee 88

M8 M8 M8 M8 Meeeeeeeee Meeee (%) Mee
MMe MMe MMM Me eeeeee, 888°M 88 [‌888‌,‌888‌]
MMe MMe MMM MM8MMMM eeeeee, 888°M 88 [‌888‌,‌888‌]
MMe MMe MM8MM=MM8 Me eeeeee, 888°M 88 [‌888‌]
MMe MMe M Me eeeeee, 888°M 88 [‌888‌]
MMe MMe MMM M eeeeee, 888°M 88 [‌888‌]
Me MMe M Me eeeeee, 888°M 88 [‌888‌]
Me MMe M MM8MMM eeeeee, 888°M 8888 [‌888‌]
Me Me MeMe8e Me MM8Me8, 88°M 88 [‌888‌]
Me MeMe MeMe8e M MM8Me8, 88°M 88 [‌888‌]
M Me-Me M Me MeMM, 88°M 88 [‌888‌]
MM=MM8 MMe M Me MeMM, 88°M 88e [‌888‌]
Me Me M Me eeeeeee, 88°M 88 [‌888‌]

e Meeeeeeee ee eeee eeee eee eeeeeee ee eeeeeeee eeee eeeeeeee(eeeeeee)eeeeeeee.

e Meeeeee eeeee eee eeeeeeee ee eeeeeeeee eee eeeeeeeeeeeee.

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Meeeee 88 Mee Meeeee ee Meeeeeeeeeee ee eee Meee ee Meeeeeeeeee ee eee Meeeeeeeeeeeee ee 8-Meeeeeeeeeeeeeeeeeeee[‌888‌,‌888‌]

Meeeeeeeeee 88

M8 M8 M8 M8 Meeee (%) Mee
888 888
MMe MMe M Me 88 88 [‌888‌]
MMe MMe M MMe 88 88 [‌888‌]
MMe MMe M MMM 88 8 [‌888‌]
MMe MMe M MM8Me 8 88 [‌888‌]
Me Me MMM Me 88 88e [‌888‌]

e Mee eeeeeeee eee eeeeeeeee ee Me8M ee eeeeee.

Meeeeeeeeee ee 8-eeeeeee-8-eeeeeeeeeeeeeeeeeeeee eeee eeeeeeee eeeeeeeeeeeeee eeeeeeeeeeee M8 ee M8 eee eeee ee eeeeeeeee eeeeeeeeeeeee 888 (Meeeee 88), eeeee eeeeeee ee eeeeeeee ee eee eeeeee-eeeeeeee eeeeeee ee e π-eeee eeeeeeeeeeee ee M8 ee M8. Meeeeeee ee eeee eeeeeeeeeeeee eeeeeeeeeee eeeeeee ee eee Meeee eeeeeeeeeee eee eeeee ee Meeeee 88.[‌888‌,‌888‌] Meee, eee eeeeeeeeeee ee e eeeeeeeeeeeee 888 eeeeeeeee ee eeeeeeeeeeee 888, eeeee eeeeeeeee Meeee eeeeeeeeeee ee eeeeeee e eeeeeeeee 888. Meee eeeee eeeeeeeee eee eeeeeeeee eeeee eeee eeeeeeee eeeeeeeeee (8.888M), eeeeeeeeeee eee ee eeeeeeee ee eee eeeeeeeeeeee eeee eeeeeeee eeeeeee ee eee eeeeee eeeeee π-eeee eeee eeeeee ee eeeeee eee eeeeeeee ee­eeeeeee 888. Meeeeeee eeee eeeeeeee eeee eeeee ee eeeeeeeeeeeeee 888 (M=M) eee eeeeeeeeeeeeeeeeee 888 (M=MMM8Me) ee eeee eeeeeee eeeeee. Me eeee eeeeeeeeeeee (8.8M) eeeeeeeee, eeeeeee, eeeeeeeeeeeeee eeeeeeee eeee eeeeeeee eeeeeeeee eee eeeeeeeeeee eeee eeeeeeeeeee ee eee eeeeeeeee 888, eee eee eeeeee eeeeeee ee eee Meeee eeeeeeeeeee, e eeeee-8,8-eeeeeee 888, ee eeee eeeeeeee ee eee eeeeeeeee eeeeeee ee eee eeeeeeee.

Meeeee 88 Meeee Meeeeeeeeee eeee Meeeeeeeee Meeeeee π-Meeeeeeeeee ee eee Meeeeeeeeeee Meee Meeeeee[‌888‌,‌888‌]

Meeeeeeeeee 88

M8 M8 M Meeee (%) Mee
888 888
MMe MMe M 8 88e [‌888‌]
MMe MMe M 88 8e [‌888‌]
MMe Me M 8 88 [‌888‌]
MMe Me M 8 88 [‌888‌]
MMe MMM MMM8Me 8 88 [‌888‌]
MMe Me MMM8Me 8 88 [‌888‌]

e Meeeeeee eeeeeeeee eeee 8.888M eeee ee 888.

e Meeeeeee eeeeeeeee eeee 8.8M eeee ee 888.

M eeeeee ee eeeee eeeee ee eeeeeeeeeee ee eee eeeeeeeeeeee eeeeeeeeee eeeeeeeee ee Meeee eeeeeeeeeee eeeeeeeee eee eeeeeeeeeeee M8 eee M8 eeee eeee eeeeeeee.[‌888‌,‌888‌,‌888‌,‌888‌] Me eeeeeeeeee eeeeeeee ee eee eeeeeee eeeeeeee ee Meeeee 88 eeeeeee ee eee eeeeeeeee ee eeeeeeeeeeeeeeeeeee-8,8-eeeeeeee 888. Meeeeeeeeee ee eee eeeeeeeeeeeeee 888 ee eeeeeee ee eeeeee eeeee eeee eeeeeeee eeeeeeeeee eeeeeeee eeeeeeeeeeeee 888, eeeee eeeeeee Meeee eeeeeeeeeee ee eeeeeeee eee eeeeeeeeee 888. M 8-eee eeeeeee eeeeeeeeeee eeee eeeee e eeeeeeee ee­eeeeeee 888, eee eeeeeeeeeeeeee eeeeeeee eeee eeeeeeee (eeeee-eeeeeeee eeeeeeeeee eeeee) eeeeeeeee e eeeeee eeeeeeeee 888, eeeee eeeeeeee ee eeee e eeeeeeeeeeeeeeeee 888.

Meeeee 88 Meeeeeeee ee Meeeeeeeeeeeeeeeeee-8,8-eeeeeeee[‌888‌]

Meeeeeeeeeee Meeeeeeee

8-Mee-8-eeee-8-eeeeeee-8,8-eeeeeeeeeeeeeeeee-8-ee-8-eee (888, M8=M8=MMe; M8=M; M8=Me); Meeeeee Meeeeeeee:[‌888‌]

M eeee ee eee-8-eee (8.88e, 8.88eeee) ee MMM (88eM) eee eeeeee ee 88°M eeeee 8.88M MeMe (8.8eM, 8.88eeee) eee eeeee eeeeeeee eee eee eeee eee eeeeeee eee 88eee. Mee eeeeeee eee eeee eeeee ee e eeee ee 8,8-eeeeeeeeeeeeeeeeeeee-8,8-eeeee (8.88e, 8.88eeee) ee MMM (88eM) eeeeeeeee ee 88°M. Mee eeeeeee eee eeeeeee ee eeee eee 88eee, eee eeee ee eee eeeeeeee eeee 8% ee MM8Me (88eM) eee eeeeeee eeee Me8M (88eM). Mee eeeeeee eeeee eee eeeeeeeee eeee Me8M (8 × 88eM), eee eee eeeeeeee eeeeeee eeeeee eeee eeeeee eeee eee. ee MeMe eeee (8 × 88eM), eeeee (MeMM8), eee eeeeeeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, MeMMe/eeeeeee 8:8) eee eeeeeeeeee eeeeeeeeeee (Me8M/eeeeeee) ee eeee eeeeeeeee eeeeee; eeeee: 8.88e (88%); ee 8888°M.

8-Meeee-8,8-eeeeeeeeeeeeee-8,8-eeeeeee (888, M8=M8=MMe; M8=M; M8=Me); Meeeeee Meeeeeeee:[‌888‌]

M eeee ee eee eeeeeeeeeeeee 888 (M8=M8=MMe; M8=M; M8=Me; 8.88e, 8.88eeee) ee e-eeeeee (88eM) eee eeeeee ee eeeeee eee 88eee eee eeee eeeeeeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, MeMMe/eeeeeee) ee eeee e eee eee; eeeee: 8.88e (88%).

8-Meeeee-8,8-eeeeeeeeeeeeee-8,8-eeeeeee (888, M8=M8 =MMe; M8=M; M8=MMe) eee 8-(Meeeeeeeeeeeeee)-8,8-eeeeeeeeeeeeeeeeee-8-eee-8,8-eeeee (888, M8=M8 =MMe; M8=M; M8=MMe); Meeeeee Meeeeeeee:[‌888‌]

M eeee ee eeeeeeeeeeeee 888 (M8=M8 =MMe; M8=M; M8=MMe) ee e-eeeeee eee eeeeee ee eeeeee eee 88eee, eee eeee eeeeeeeeeeee ee 88°M. Mee eeeeeee eee eeeeeee eeee Me8M eee eeeeee eeee e eeee ee Me8M8M8 ee M8M. Mee eeeeeee eeeee eee eeeeeeeee eeee Me8M, eee eee eeeeeeee eeeeeee eeeeee eeee eeeeee eeee eee. eeeee, eeeee (MeMM8), eee eeeeeeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee ee eeeeeee eee eeeeee: eee eeeee-8,8-eeeeeee 888 (M8=M8 =MMe; M8=M; M8=MMe); eeeee: 8.888e (88%); ee 8888.8°M, eee eee eeeeeeeee-8-eee-8,8-eeeee 888 (M8=M8 =MMe; M8=M; M8=MMe); eeeee: 8.888e (88%); ee 88°M.

(8M)-8,8-Meeeeeeee-8-(eeeeeeeeeeeeeeee)-8,8-eeeeeee-8M-8-eeeeeeeeee-8,8-eeeee (888, M8=M8=MMe; M=M); Meeeeee Meeeeeeee:[‌888‌]

M eeee ee eee eeeeeeeeeeeee 888 (M8=MMe; M8=MMe; M=M; 8.888e, 8.88eeee) ee eeeeeee (888eM) eee eeeeee ee eeeeee eee 8e, eee eeee eeeeeee ee eeee ee ee. Meeee eeeeeeeeeeeee, eee eeeeeee eee eeeeeeee ee eeeeeeeeeeeeee (eeeeee eee, MeMMe/eeeeeee 8:8) ee eeee e eee eeeee; eeeee: 8.888e (88%); ee 8888°M.