Synthesis of tetracyclic chromenones via platinum(ii) chloride catalysed cascade cyclization of enediyne–enones

Abstract

PtCl2 catalysed cascade cyclization of an enediyne-enone system to afford a tetracyclic chromenone is reported, which proceeds through two consecutive highly regioselective 6-endo-dig cyclizations in a single step with the formation of two new C-C bonds and two new rings in excellent yield. A mechanism for this transformation is proposed based on the isolated intermediates.

(Hetero)aromatics from dienynes, enediynes and enyne–allenes

“…The proposed mechanism involved the initial coordination of the catalyst by one of the triple bonds of 115a-c to afford complexes 116a-c. Then, 6-endo-dig cyclization of the enone moiety occurred followed by deprotonation leading to intermediates 117 À a-c. Protodemetallation of 117 À a-c to 118a-c and ensuing coordination of the remaining triple bond by the catalyst afforded 119a-c. A second 6-endo-dig cyclization of the electron rich C5 pyran carbon onto the activated alkyne gave intermediates 120 À a-c, which further underwent protodemetallation to give the final products 121a-c (Scheme 32). 151 The same catalyst has been employed in the synthesis of benzo-and naphthopyranones from the corresponding enediynes. 152 Treatment of 1,2-bis(ethynyl)arenes with hydrohalic acids in the presence of 5-10 mol% of Pt II Cl 2 led to the formation of the corresponding 1-halonaphthalenes.…”

“…83 Similarly, the Pt II Cl 2 -catalyzed cyclization cascade of enediyneenone systems has been recently described. 151 By following this approach, tetracyclic chromenones were obtained in excellent yields through two consecutive, highly regioselective, 6-endo-dig cyclizations, where two new C-C bonds and two new rings were formed. The proposed mechanism involved the initial coordination of the catalyst by one of the triple bonds of 115a-c to afford complexes 116a-c. Then, 6-endo-dig cyclization of the enone moiety occurred followed by deprotonation leading to intermediates 117 À a-c. Protodemetallation of 117 À a-c to 118a-c and ensuing coordination of the remaining triple bond by the catalyst afforded 119a-c. A second 6-endo-dig cyclization of the electron rich C5 pyran carbon onto the activated alkyne gave intermediates 120 À a-c, which further underwent protodemetallation to give the final products 121a-c (Scheme 32).…”

Gold-catalysed reactions of diynes

“…Wang's group demonstrated that 1,2-dialkynylarenes 96 with carboxylic acids offered as intramolecular nucleophiles Also a donor-acceptor-substituted olefin can serve as a nucleophile, but this is only briefly mentioned in a publication of Perumal's group. 74 With a 1,5-diyne-ene and 5 mol% AuCl 3 in toluene 30% yield of the product of the ene-yne cyclisation was isolated. With 5 mol% Ph 3 PAuCl and 10 mol% AgBF 4 in toluene 32% of the product of the two-fold cyclisation involving both alkynes and the alkene could be isolated.…”

Ring-Closing Metathesis of Co2(CO)6–Alkyne Complexes for the Synthesis of 11-Membered Dienediynes: Overcoming Thermodynamic Barriers

“…IR (KBr, thin film) ν max (cm −1 ): 3083,3062,3014,2981,2922,2222,1641,1459,1433,1415,1363,1320,1284,1217,1160,1131,1067,1016,989,917,853,803,753,730. MS (EI, 70 eV), m/z: 262 (26, M + ), 234 (5), 222 (11), 221 (12), 205 (19), 195 (10), 175 (8), 153 (9), 58 (37) ), 5.10 (dq, 3 J = 10.2, 4 J = 2 J = 1.1, 1H, CH B ), 5.15−5.24 (m, 2H, CH A , CH B ′), 5.51 (dq, 3 J = 17.0, 4 J = 2 J = 1.8, 1H, CH A ′), 5.88−6.05 (m, 2H, CH X , CH X ′), 7.35−7.42 (m, 2H, H Ar ), 7.69−7.71 (m, 1 H, H Ar ), 7.82−7.84 (m, 1 H, H Ar ). 13 C NMR (100 MHz, CDCl 3 , δ): 19.7 (s), 24.3 (s), 33.0 (s), 74.3 (q), 76.1 (q q ), 96.2 (q), 96.7 (q), 115.9 (s), 116.7 (s), 122.0 (t), 122.7 (q), 123.3 (t), 124.9 (t), 125.7 (q), 125.8 (t), 131.5 (t), 136.9 (t), 138.1 (q), 139.0 (q).…”

“…Naturally occurring macrocyclic enediyne antibiotics are well-known as potent anticancer agents, and a broad range of synthetic analogues of these compounds have been synthesized and investigated by our colleagues in the synthetic community. − Recently, enediyne systems have widely been utilized as sequence intermediates in organic synthesis for construction of polycyclic molecules, − natural products, and polymer materials and have also been used themselves in the role of catalysts . In the search among synthetic analogues of naturally occurring enediynes for new molecules possessing antineoplastic activity, only cyclic enediynes incorporated into 9- or 10-membered cycles are considered valid targets.…”