Fully Substituted Conjugate Benzofuran Core: Multiyne Cascade Coupling and Oxidation of Cyclopropenone

Abstract

An unprecedented CC double bond cleavage of cyclopropenone and dioxygen activation by multiyne cascade coupling has been developed. This chemistry provides a novel, simple, and efficient approach to synthesize fully substituted conjugate benzofuran derivatives from simple substrates under mild conditions. The density functional theory (DFT) calculations reveal that the unique homolytic cleavages of cyclopropenone and molecular oxygen are crucial to the success of this reaction.

DMAP‐Catalyzed [3+3] Annulation of Cyclopropenones with α‐Bromoketones for Synthesis of 2‐Pyrones

“…While Na 2 CO 3 , NEt 3 , and 1,8diazabicyclo[5.4.0]undec-7-ene (DBU) could not promote the reaction, Cs 2 CO 3 , NaH, t BuOK, and KOH readily facilitated the [3 + 3] annulation to give product 3 a, with KOH being the best choice regarding the yield given (43 % yield) (entries 1-7). Other Lewis base catalysts such as PMe 3 , PBu 3 , P(4-MeOC 6 H 4 ) 3 , P(4-MeC 6 H 4 ) 3 , 1,4-diazabicyclo [2.2.2]octan (DABCO), and 4-dimethylaminopyridine (DMAP) were examined, among which DMAP stood out to provide 3 a in 60 % yield (entries [8][9][10][11][12][13]. When the amounts of 2 a and KOH were increased to 1.5 equiv, the reaction yield upgraded to 72 % (entry 14).…”

“…Substrate 1 a was commercially purchased, while 1 b, [12] 1 c, [13] 1 d, [13] and 1 e [14] were prepared according to reported methods. 1 H, 13 C, and 19 F NMR spectra were recorded on Bruker AV400 or JNM-ECZ400S/L1 400 MHz spectrometers. Chemical shifts (δ values) were reported in ppm with TMS ( 1 H NMR) and CDCl 3 ( 13 C NMR) as internal standard, respectively.…”

“…Unless otherwise noted, all reactions and manipulations were performed in nitrogen atmosphere under anhydrous conditions using standard Schlenk techniques. Substrate 1 a was commercially purchased, while 1 b, [12] 1 c, [13] 1 d, [13] and 1 e [14] were prepared according to reported methods. 1 H, 13 C, and 19 F NMR spectra were recorded on Bruker AV400 or JNM-ECZ400S/L1 400 MHz spectrometers.…”

“…1 H NMR (400 MHz, CDCl 3 ): δ 8.03 (d, J = 8.2 Hz, 2H), 7.74 (d, J = 8.3 Hz, 2H), 7.32-7.15 (m, 10H), 6.93 (s, 1H). 13 C NMR (100 MHz, CDCl 3 ): δ 162. 2, 156.3, 152.2, 137.3, 134.5, 133.4, 132.1 (q, J C-F = 32.8 Hz), 130.7, 128.9, 128.6, 128.4, 128.0 127.9, 126.0, 125.9 (d, J C-F = 3.5 Hz), 125.7, 124.3, 123.7 (q, J C-F = 272.2 Hz), 106.3.…”

“…1 H NMR (400 MHz, CDCl 3 ): δ 7.25-7.07 (m, 10H), 6.13 (s, 1H), 2.49 (t, J = 11.6 Hz, 1H), 2.07 (d, J = 13.2 Hz, 2H), 1.86 (d, J = 12.9 Hz, 2H), 1.75 (d, J = 15.2 Hz, 1H), 1.57-1.18 (m, 5H). 13 C NMR (100 MHz, CDCl 3 ): δ 167.9, 163. 6, 152.8, 138.0, 134.1, 130.9, 128.8, 128.6, 128.3, 128.0, 127.6, 122.2, 104.5, 42.3, 30.7, 26.0, 25.9.…”