Weakly Coordinating tert-Amide-Assisted Ru(II)-Catalyzed Synthesis of Azacoumestans via Migratory Insertion of Quinoid Carbene: Application in the Total Synthesis of Isolamellarins

Abstract

A weakly coordinating tert-amide-directed straightforward method was developed for the synthesis of azacoumestans using the corresponding azaheterocycle derivatives and diazonaphthoquinones under cheap Ru(II)-catalyzed conditions. The reaction proceeds via migratory insertion of quinoid carbene and subsequent Brønstead acid-mediated cyclization. The optimized C2-selective method offered a wide scope of important azaheterocycles. Bioactive natural products like isolamellarins A and B were synthesized via the developed protocol. Preliminary mechanistic studies highlighted the probable mechanistic pathway.

Rhodium-Catalyzed Tandem C–H Annulation Enabled by Transient Directing Group Strategy and Sequential Nucleophilic Substitution

“…On the basis of the forementioned results and previous literature, − , a plausible mechanism was proposed (Scheme ). Initially, intermediate I is formed by anion exchange of [Cp*RhCl 2 ] 2 with AgSbF 6 and carboxylic acid via Cl – extraction.…”

“…In 2017, the Cui group developed a rhodium-catalyzed tandem C–H activation of benzamides with diazonaphthalen-2­( 1H )-ones for the synthesis of lactones . Recently, the Samanta group disclosed a similar methodology by using ruthenium as the catalyst (Scheme C) . These one-pot constructions of C–C/C–O bonds with diazonaphthalen-2­( 1H )-ones offer an opportunity to realize the synthesis of 6 H -benzo­[ c ]­chromen-6-ol via tandem C–H activation by using aldehyde as the directing group.…”

Green and Efficient Construction of Chromeno[3,4-c]pyrrole Core via Barton–Zard Reaction from 3-Nitro-2H-chromenes and Ethyl Isocyanoacetate

“…The chromenopyrrole moiety is present in a wide range of natural and synthetic compounds with a number of important useful properties [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. Thus, chromeno[3,4- b ]pyrrole scaffold is the basis of the skeleton of type I lamellarin alkaloids isolated from marine mollusks, tunicates and sponges [ 1 , 2 ] ( Figure 1 ).…”

“…Pericyclic pyrrolo[3,4- c ]coumarin 4 emits blue light and may be tested as blue-light emitters with an electron-transporting ability [ 10 ] ( Figure 1 ). In view of the above, the development of methods for the synthesis of these classes of compounds is being carried out by various scientific groups, and the search for new effective approaches to the design of chromenopyrrole scaffolds continues [ 11 , 12 , 13 , 14 , 15 ].…”

Rh(III)-Catalyzed Weakly Coordinating 2-Pyridone-Directed Oxidative Annulation Using Internal Alkynes: A Reversal in Selectivity

“…Intrigued by our previous studies of transition metal-catalyzed 2-pyridone functionalizations , and weakly coordinating group-directed C–H bond functionalization, we hypothesized that the carbonyl group in the 2-pyridone ring might play the role of an intrinsic directing group for the Satoh–Miura type annulation at the aryl ring with the internal alkynes. The selection of proper conditions might offer the desired annulated product.…”