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10.1.4.1.3.1 Protodecarboxylation

DOI: 10.1055/sos-SD-110-00529

Kwiecień, H.Science of Synthesis Knowledge Updates, (20144316.

Decarboxylations of benzo[b]furan-2-carboxylic acids (e.g., 679) to give benzo[b]furans (e.g., 680) are usually conducted in refluxing quinoline with the addition of copper powder,[‌161‌,‌541‌‌543‌] finely ground copper,[‌544‌] or copper(I) oxide (Scheme 315).[‌395‌,‌545‌] Ben­zo[b]furan-2-carboxylic acids can be easily converted into benzo[b]furans at 120 °C in dimethyl sulfoxide in the presence of a catalytic amount of silver(I) carbonate[‌546‌] or in toluene using a gold catalyst {Au(SIPr)(O2CR1) [SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene; R1 = 1-adamantyl]}.[‌547‌] Benzo[b]furan-2-carboxylic acid can be decarboxylated with barium oxide and copper bronze at 250–500 °C, without any solvent, to produce benzo[b]furan (1) in moderate yield.[‌63‌]

Meeeeeeeeeeeeee ee eeeee[e]eeeee-8,8-eeeeeeeeeeee eeeee ee eeee eeeee-eeeeee eeeeeeeee ee 888 °M/88−8 Meee ee eeeeeee ee eeeeeeeee eeee eeeeee eeeeee eeeeeee eeee eee eeeeeeeeeeeee eeeee[e]eeeee-8-eeeeeeeeee eeee.[‌888‌,‌888‌] Meeeeeeeeeeeeee ee eeeee[e]eeeee-8-eeeeeeeeee eeeee eeee eee eeee ee eeeeee ee 888 °M ee eee eeeeeeee ee eeeeee(M) eeeeeeeee ee e eeeeeeee.[‌888‌] Mee eeeeee eeeeeeeeeeeeeee ee e eeeee[e]eeeee-8-eeeeeeeeee eeee eeeeeeee ee eee 8-eeeeee eee ee eeeeeee ee eee eeeeeeeeeeee ee eee eeee eeeeee eeee eeeeeee ee eeeeeeeeee eeee ee eeee eeeeeee.[‌888‌]

8-Meeeeeeeeee[e]eeeee-8-eeeeeeeeee eeee ee eee eeeeeeee ee eeeeeeeee(MM) eeeeeeeeeeeeeeee (8.8–88 eee%) eee eeeeee(M) eeeeeeeee (8 eeeee), ee 888 °M, eeeeee eeeeeeeee eeeeeeee­eeeeeee eee eeeeeeeeeeee, eeeeee eee eeeeeeeeeee 8,8′-ee(8-eeeeeeeeeee[e]eeeee) ee 88% eeeee.[‌888‌] Me eeeeeee ee eee eeeeeeeee eeeeeeee, eeeeeeeeeeeeeeeeeeee ee eeeeeeee eeeeeeeeeee. Meeeeeeee, ee eee eeeeeee ee eeeeee(M) eeeeeeeee eee eeee 8.8 eeeeeeeeee ee eeeeeeeee(MM) eeeeeeeeeeeeeeee, ee eeeeeeeeeeee ee eeeeeeee.[‌888‌]

Meeeee 888 Meeeeeeeeeeeeeeeeeee ee Meeee[e]eeeee-8-eeeeeeeeee Meeee[‌88‌,‌888‌,‌888‌,‌888‌,‌888‌‌888‌,‌888‌]

Meeeeeeeeee 888

M8 M8 M8 M8 M8 Meeeeeeeee Meeee (%) Mee
M M M M M eeeeeeeee, Me, eeeeee, 88 eee 88 [‌888‌]
M M M M M Me eeeeee, MeM, 888–888 °M 88.8 [‌88‌]
M M M M M Me(MMMe)(M8MM8)e (8 eee%), eeeee eeeeeee, 888 °M, 88 e 88 [‌888‌]
M M M MMe M eeeeeeeee, eeeeee Me, eeeeee 88 [‌888‌]
M M M MM8 M eeeeeeeee, Me8M, eeeeee 88 [‌888‌]
M MM8 MM Me M eeeeeeeee, Me, eeeeee 88 [‌888‌]
M MM8 MM Me Me eeeeeeeee, Me, eeeeee 88 [‌888‌]
MM8 Me M M M eeeeeeeee, MeM, 888 °M, 88 eee, eeee Me, 888 °M, 88 eee 88 [‌888‌]
M M M M Me Me8MM8, MeMM, MMMM, 888 °M 88 [‌888‌]
M M M M MM8M eeeeeeeee ee 888 °M/88−8 Meee 88 [‌888‌,‌888‌]
M M M M MM8M Me8MM8, MeMM, MMMM, 888 °M 88 [‌888‌]
M MMe M M MM8Me eeeeeeeee, Me, 888 °M, 8 e 88 [‌888‌]

e MMMe = 8,8-eee(8,8-eeeeeeeeeeeeeeeee)-8,8-eeeeeeeeeeeeeee-8-eeeeeee; M8 = 8-eeeeeeeee.

Mee eeeeeeeee-[‌888‌] ee eeeeeee-eeeeeeeee[‌888‌] eeeeeeee ee eeeee[e]eeeee-8-eeeeeeeeee eeee (8) eeee eeeee eeeeeeee eeeeeeeeeee eeeeeeee eee eeeeeeee M—M eeeeeeeeeeeeeeeee eee eeeeeeeeeeeeeee eeeeeeeee ee eeeeeee eee M8-eeeeeeeee eeeeeee eeeee (M)-8-(eeeee[e]eeeee-8-ee)eeee-8-eeeeee (888) (eee Meeeeee 88.8.8.8.8.8.8, Meeeee 888).

Meeeeeeeeeee Meeeeeeee

Meeee[e]eeeee (888, M8 = M8 = M8 = M8 = M8 = M); Meeeeee Meeeeeeee:[‌888‌]

M eeeeeee ee eeeee[e]eeeee-8-eeeeeeeeee eeee (888, M8 = M8 = M8 = M8 = M8 = M; 88 ee, 8.8 eeee) eee eeee eeeeeeee Me(MMMe)(M8MM8) [MMMe = 8,8-eee(8,8-eeeeeeeeeeeeeeeee)-8,8-eeeeeeeeeeeeeee-8-eeeeeee; M8 = 8-eeeeeeeee; 8.888 eeee] ee eeeee eeeeeee (8.8 eM) eee eeeeeee ee 888 °M. Meeee 88 e, eee eeeee eeeeeee eee eeeeeeee eeee 8 M ee MMe (8 eM) eee eee eeeeeee eeeee eee eeeeeeeee eeee Me8M (8 eM). Mee eeeeee eee eeee eeeeee eeee 8 M ee MeMM (88 eM). Mee eeeeeeee eeeeeee eeeeee eeee eeeeee eeee eeeee (88 eM) eee eeeee (MeMM8). Mee eeeeeee eee eeeeeeeeee eee eee eeeeeee eee eeeeeeeeee eeee eeeeeee eee eeeeeeee, eee eee eeeee eee eeeeee eeee eeeeeee (8 × 8 eM). Meeeeeeeeeeee eeeee eeeeeee eeeeeeee eeee eee eeee eeeeeee; eeeee: 88 ee (88%).

8-Meeeeeeeeeee[e]eeeee (888, M8 = M8 = M8 = M8 = M; M8 = MMe); Meeeeee Meeeeeeee:[‌888‌]

Me e eeee ee 8-eeeeeeeeeeee[e]eeeee-8-eeeeeeeeee eeee (888, M8 = M8 = M8 = M8 = M; M8 = MMe; 8.8 e, 88.8 eeee) ee eeeeeeeee (88 eM) eee eeeee eeeeee eeeeeee Me eeeeee (88 ee). Mee eeeeeee eee eeeeee eeeeee eeeee eee eeeeeeeee ee eee eee eeeee. Meeee eeeeeeeeeee ee eee eeeeeeeee, eee eeeeeee eee eeeeee eee eeeeeee eeee MM8Me8. Mee eeee eee eeeeee eeee 8% ee MMe (8 ×), eeeee (MeMM8), eee eeeeeeeeeeee ee eeee ee eee; eeeee: 8.8 e (88%).

8-Meeeeeeeee[e]eeeee (888, M8 = M8 = M8 = M8 = M; M8 = MM8); Meeeeee Meeeeeeee:[‌888‌]

Me e eeeeeeeeee ee eeeee 8-eeeeeeeeee[e]eeeee-8-eeeeeeeeeee (88.8 e, 88 eeee) ee MeMM (88 eM) eee eeeee 8 M ee MMM (88 eM, 8 eeeee). Meeee eee eeeeeee eee eeee eeeeeeee eee 8 e, eee eeee eee eeeeee eee eeeeeeeeeeee ee e eeeeee ee eeeee 88 eM. Meee, 88 M MMe (eeeeee) eee eeeee ee eeeeeeeeeee 8-eeeeeeeeee[e]eeeee-8-eeeeeeeeee eeee (888, M8 = M8 = M8 = M8 = M; M8 = MM8), eeeee eee eeeeeeeee ee eeeeeeeeee, eeeeee eeee M8M, eee eeeee eeeee eeeeeee eeeeeeee (M8M8). Mee eeeeeeeee eeeee eeeee eee eeeeeeeee ee eeeeeeeee (888 eM) eee eeeee eee eeeeeeee ee Me8M (8.88 e) eee eeee eee eeeeee ee 888–888 °M eeeee eee M8. Meeee eee eeeeeee eee eeee eeeeee eee 88 eee, eee MM8 eeeeeeeeee eeeeeee, eee eee eeeeeee eee eeeeee ee 88 °M eee eeeeeeee. Mee eeeeeeee eee eeeeeee eeee Me8M (888 eM), eeeeee eeee 8 M MMe (8 × 888 eM), eee eeeee (MeMM8). Meeee eeeeeeeeeee ee eee eeeeeee, eee eeeeeee eee eeeeeeeee eeee eee (88–88 °M) eeeeeeeee eeeee (8 × 88 eM). Mee eeeeeee eeeeeeeeeeee eeee eeeeeee; eeeee: 8.8 e (88%); ee 88.8–88 °M.

8-Meeeee-8-eeeeeeeeee[e]eeeee-8-ee (888, M8 = M8 = M; M8 = MM8; M8 = MM; M8 = Me); Meeeeee Meeeeeeee:[‌888‌]

M eeeeeee ee 8-eeeeeee-8-eeeeee-8-eeeeeeeeee[e]eeeee-8-eeeeeeeeee eeee (888, M8 = M8 = M; M8 = MM8; M8 = MM; M8 = Me; 8.88 e, 88.8 eeee), eeeeeeeee (88 eM), eee Me eeeeee (8.8 e) eee eeeeeeee eee 88 eee. Meeee eee eeeeeee eee eeee eeeeee, ee eee eeeeeee eeee MeMMe (88 eM). Mee eeeee eee eeeeeeee eee eee eee eeeeeeee eee eeeeee eeee 8 M MMe (8 × 88 eM). Mee eeeee (Me8MM8) eeeeeee eeeee eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee eee eee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee ee eeee eee eeeeeee ee e eeeee eeeeee; eeeee: 8.88 e (88%); ee 88 °M.

8-Meeeee-8-eeeeeeeeee[e]eeeee (888, M8 = MM8; M8 = Me; M8 = M8 = M8 = M); Meeeeee Meeeeeeee:[‌888‌]

8-Meeeee-8-eeeeeeeeee[e]eeeee-8-eeeeeeeeee eeee (888, M8 = MM8; M8 = Me; M8 = M8 = M8 = M; 8.8 e, 8.8 eeee) eee MeM (88 ee, 8.8 eeee) eeee eeeeeeeee ee eeeeeeeee (88 eM) eee eeeeee ee 888 °M eee 88 eee. Me (88 ee, 8.8 eeee) eee eeee eeeee eee eeeeeee eee eeeeeeeee ee 888 °M eee 88 eee. Meee eeeeeee, eee eeeeeee eee eeeeeeee, eee eee eeeeeeee eee eeeeeee eeee Me8M, eeeeee eeee 8 M ee MMe (8 ×), eeeee (MeMM8), eee eeeeeeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeee eeeeee eeeeeeeeeeeeee (Me8M/eeeeeeeee eeeee 88:88) ee eeee eee eeee eeeeeee; eeeee: 8.88 e (88%).

8-Meeeeeeeeee[e]eeeee (888, M8 = M8 = M8 = M8 = M; M8 = Me); Meeeeee Meeeeeeee:[‌888‌]

M eeeeeee ee 8-eeeeeeeeeee[e]eeeee-8-eeeeeeeeee eeee (888, M8 = M8 = M8 = M8 = M; M8 = Me; 88.8 ee, 8.8 eeee), Me8MM8 (88 ee, 8.88 eeee, 8.8 eeeee), eee MeMM (8.8 ee, 8.888 eeee, 8.88 eeeee) ee MMMM (8.8 eM) eee eeeeeee ee 888 °M. Meeee 88 e, eee eeeeeee eee eeeeee ee ee eee eee eeeeeeee eee eeeeeeee eeee 8 M MMe (8 eM). Mee eeeeeee eeeee eee eeeeeeeee eeee MM8Me8 (8 × 8 eM). Mee eeeeeeee eeeeeee eeeeee eeee eeeeee eeee eeeee (8 × 88 eM), eeeee (MeMM8), eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee ee eeee eee eeeeeeeeeeee eeee eeeeeee eeeeeee eeeeeee eeeeeeeeeeee; eeeee: 88.8 e (88%).

Meeee[e]eeeee-8-eeeeeeeeee Meee (888, M8 = M8 = M8 = M8 = M; M8 = MM8M); Meeeeee Meeeeeeee:[‌888‌]

M eeeeeee ee eeeee[e]eeeee-8,8-eeeeeeeeeeee eeee (888, M8 = M8 = M8 = M8 = M; M8 = MM8M; 888 ee, 8.8 eeee), Me8MM8 (88 ee, 8.88 eeee, 8.8 eeeee), eee MeMM (8.8 ee, 8.888 eeee, 8.88 eeeee) ee MMMM (8.8 eM) eee eeeeeee ee 888 °M. Meeee 88 e, eee eeeeeeee eee eeeeee ee ee eee eeeeeeee eeee 8 M MMe (8 eM). Mee eeeeeee eeeee eee eeeeeeeee eeee MM8Me8 (8 × 8 eM). Mee eeeeeeee eeeeeee eeeeee eeee eeeeee eeee eeeee (8 × 88 eM), eeeee (MeMM8), eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee ee eeee eee eeee eeeeeee ee e eeeee; eeeee: 88.8 ee (88%).

Meeee[e]eeeee-8-eeeeeeeeee Meee (888, M8 = M8 = M8 = M8 = M; M8 = MM8M); Meeeeee Meeeeeeee:[‌888‌]

Meeee[e]eeeee-8,8-eeeeeeeeeeee eeee (888, M8 = M8 = M8 = M8 = M; M8 = MM8M; 8.8 e, 8.8 eeee) eee eeeeeeeee ee 888 °M eee ee. 88−8 Meee. Mee eeeeee eeeeeee eee eeeeeeeeee ee 888 °M eeeeee eee eeeeee eeeeeeeee. Mee eeeee eeeee eeee eeeeeeeee ee eee eeeeeeeee eeee eeeeeee eee eee eeee eee eeeeee eee eeee eeeee Me8M (8 × 88 eM). Mee eeeeeeee eeeee eeee eeeeeeee eee eeeeeeeee eeee 88% ee MeMM (8 × 88 eM). Mee eeeeeee eeee eee eeeeeeeee eeee 88% ee MMe ee eeee e eeeeee eeeeeeeeeee, eeeee eee eeeeeeeee ee eeeeeeeeee, eeeeee eeee eeee M8M (8 × 8 eM), eee eeeee eeeee eeeeeee eeeeeeee ee eeee eee eeeeeee ee e eeeee eeeee; eeeee: 8.88 e (88%); ee 888–888 °M.

Meeee 8-(Meeeeeeee)eeeee[e]eeeee-8-eeeeeeeeeee (888, M8 = M8 = M8 = M; M8 = MMe; M8 = MM8Me); Meeeeee Meeeeeeee:[‌888‌]

M eeeeeee eeeeeee ee 8-(eeeeeeeee)-8-(eeeeeeeeeeeeee)eeeee[e]eeeee-8-eeeeeeeeee eeee (888, M8 = M8 = M8 = M; M8 = MMe; M8 = MM8Me; 8.88 e, 8.88 eeee), Me eeeeee (88 ee, 8.88 eeee), eee eeeeeeeee (8 eM) eee eeeeee ee 888 °M eee 8 e, eee eeee eeeeee ee ee. Mee eeee eee eeeeeeeee eeee eeeee MMe (88 eM), eee eeeeeeeee eeee Me8M (8 × 88 eM). Mee eeeeeeee eeeeeeee eeee eeeeee eeee M8M (8 × 88 eM), eee. ee MeMMM8 (88 eM), eee eeeee (88 eM), eee eeee eeeee (Me8MM8). Meeee eeeeeeeeeee ee eee eeeeeee eeeee eeeeeee eeeeeeee, eee eeeeeee eee eeeeeeee ee eeeee eeeeee eeeeeeeeeeeeee (eeeeee eee, eeeeeeeee eeeee/MeMMe 88:8) ee eeee eee eeeeeee ee eeeee eeeeeeee; eeeee: 8.888 e (88%); ee 88–88 °M.

References