Tungsten-Catalyzed Heterocycloisomerization Approach to 4,5-Dihydro-benzo[b]furans and -indoles

Abstract

A W(CO)(5)·THF-catalyzed cycloisomerization of bicyclo[4.1.0] substrates to afford mono C4-substituted 4,5-dihydro-benzo[b]furans and -indoles is reported. The title compounds are versatile intermediates that lead to a range of fused bicycles including the cores of various furan-, benzofuran-, and indole-containing natural products. In many cases, the functionalization of the dihydro-benzo[b]furans and -indoles is orthogonal to that of the corresponding benzofurans and indoles and, thus, offers complementary approaches for synthesis.

Ein neues goldenes Zeitalter in der Chemie Donor‐Akzeptor‐substituierter Cyclopropane

“…[27] Eine aktuelle Arbeit nutzt dies in der Synthese beider Enantiomere des Naturstoffes Arteludovicinolid A (21). [29] Nach erfolgter Ringçffnung zum Carbaldehyd 20 unter nahezu vollständigem Erhalt der Stereoinformation konnte der Naturstoff 21 in nur neun Stufen ausgehend vom Furan-Derivat 18 aufgebaut werden (Schema 5).…”

Indoles via Dehydrogenation of Pyrroles

“…This method was used in a formal synthesis of chuangxinmycin. As we have seen, a large number of pyrrole → indole dehydrogenations involved the use of a benzoquinone, usu ally DDQ, and a selection of the substrates that were converted to indoles is summarized in Scheme 4 [20][21][22][23][24][25][26][27][28][29]. A new synthesis of N-substituted 7-keto-4,5,6,7-tet rahydroindoles was described by Montalban and coworkers, and these compounds along with the 4-keto analogues were aromatized to the 7-and 4-hydroxyindoles via a halogena tion/dehydrohalogenation protocol (equation 4) [19].…”

Deconstructive Reorganization: De Novo Synthesis of Hydroxylated Benzofuran

“…As for the synthesis of benzofuran, mostly pericyclic reactions and transition metal‐catalyzed cyclizations were applied to forge the benzene moiety. For comparison, more studies have been devoted to the construction of the furan moiety by formal [3+2] cycloadditions or intramolecular ring‐closure reactions with prefunctionalized phenols,–– quinones, or phenolic ethers as starting materials –. Of all these methods, the alkyne‐based benzofuran synthesis shows many benefits such as easy availability and versatile reaction types, but usually a phenolic hydroxyl group of the starting material needs to be sacrificed –.…”