Iron‐Catalyzed Synthesis of Indenones through Cyclization of Carboxamides with Alkynes

Abstract

The iron/diphosphine‐catalyzed annulation of a carboxamide possessing a bidentate directing group with an internal alkyne proceeds in the presence of phenylzinc halide as a base at 40 °C to produce a variety of indenone derivatives. The reaction proceeds through iron‐catalyzed C−H bond activation of the carboxamide, followed by insertion of the alkyne into the resulting iron intermediate, and cyclization accelerated by the presence of Lewis acidic ZnII. The reaction of naphthalene and anthraceneamide yields π‐conjugated indenone derivatives.

Mechanochemical Solvent-Free Synthesis of Indenones from Aromatic Carboxylic Acids and Alkynes

“…The new products ( 3ha , 3ka , 3ma , and 3oa – qa ) were characterized by 1 H NMR, 13 C NMR, and ESI-TOF spectra. Other products are known compounds and were characterized by 1 H NMR and 13 C NMR spectra, which were consistent with those described in the literature. ,− ,,− …”

“…Ethyl acetate/petroleum ether = 1:100 as an eluent; red solid, mp 124–125 °C (lit . 122–124 °C); 66% yield (115.2 mg); 1 H NMR (400 MHz, CDCl 3 ) δ 7.57 (d, J = 7.0 Hz, 1H), 7.41 (d, J = 8.5 Hz, 2H), 7.37 (d, J = 7.2 Hz, 1H), 7.33–7.27 (m, 3H), 7.25 (d, J = 8.6 Hz, 2H), 7.18 (d, J = 8.6 Hz, 2H), 7.10 (d, J = 7.2 Hz, 1H); 13 C­{ 1 H} NMR (100.6 MHz, CDCl 3 ) δ 195.9, 154.4, 144.7, 135.6, 134.1, 133.8, 131.6, 131.3 (2C), 130.9, 130.6, 130.2 (2C), 129.5 (3C), 129.0, 128.6 (2C), 123.4, 121.3.…”

“…Ethyl acetate/ petroleum ether = 1:50 as an eluent; red solid, mp 162−163 °C (lit. 15 163−165 °C); 30% yield (46.9 mg) from p-MeO-C 6 H 4 CO 2 H and 69% yield (107.5 mg) from m-MeO-C 6 H 4 CO 2 H; 1 H NMR (400 MHz, CDCl 3 ) δ 7.41−7.34 (m, 5H), 7.26−7.21 (m, 5H), 7.18 (d, J = 2.3 Hz, 1H), 7.03 (d, J = 8.0 Hz, 1H), 6.78 (dd, J = 8.0, 2.3 Hz, 1H), 3.84 (s, 3H); 13 C{ 1 H} NMR (100.6 MHz, CDCl 3 ) δ 196.3, 161. 2, 156.5, 137.0, 133.1, 133.1, 131.5, 131.1, 130.0 (2C), 129.4, 128.7 (2C), 128.6 (2C), 128.2 (2C), 127.6, 122.4, 116.4, 110.7, 55.9.…”

A Guide to Directing Group Removal: 8‐Aminoquinoline

“… [103] However, as discussed above (Section 1.1.1.2, Scheme 14), the AQ directing group is extremely resistant to cleavage from these products. The authors found that in the absence of an oxidant, C−C bond formation with concomitant loss of AQ was favored over C−N bond formation, giving indenones 154 in good to excellent yields [104] . Ortho ‐substituents on the benzamide moiety shut down the reaction almost completely.…”

Tris(acetylacetonato) Iron(III): Recent Developments and Synthetic Applications

“…The use of aminoquinoline carboxamides 98 established the possibility to perform directed iron-catalyzed C-H bond activation, which was reported by Nakamura for the preparation of disubstituted indenones 99 in moderate to very good yields (Scheme 11, b). 33 Scheme 8 (a) Alkenylation of cyclic ethers, 24 (b) alkenylation of cycloalkanes by Pan, 25 and (c) peroxide-mediated C-3-functionalization of flavones; 26…”