Biomimetically Inspired, One-Step Synthesis of Exotine A and Exotine B

Cyclohepta[b]indole Core Construction via the Michael Addition/Friedel-Crafts Condensation Sequence

An approach to cyclohepta[b]indoles via the formal (4 + 3) annulation of readily synthesized 2-indolyl-derived 1,3-dicarbonyl compounds to acrolein and enones was developed. The process is initiated by catalytic Michael addition, wherein the adduct was generated in situ. The subsequent addition of a Bro̷nsted acid catalyst triggers a cascade process that includes intramolecular Friedel-Crafts hydroxylalkylation followed by dehydration. The cascade reaction is relatively undemanding since even degrading chloroform is able to initiate it. The obtained tetrahydrocyclohepta[b]indoles were prone toward easy dimerization, underscoring the high reactivity of the double bond in the seven-membered ring.

Novel One-Step Total Synthesis of trans-Dehydroosthol and Citrubuntin

Efficient and simple syntheses of trans-dehydroosthol and citrubuntin were achieved in a single step by implementing a protecting-group-free, redox-neutral strategy that utilized readily available starting materials. In this approach, a practical one-pot (domino) Heck/dehydration reaction was carried out utilizing less reactive bromocoumarin, resulting in excellent stereoselectivity and atomic economy. Through the implementation of this new, efficient, and scalable synthesis method, the formal synthesis of a series of novel meroterpenoid natural products was successfully achieved.

Gold/scandium bimetallic relay catalysis of formal [5+2]- and [4+2]-annulations: access to tetracyclic indole scaffolds

Regiodivergent formal [5+2]- and [4+2]-annulation reactions of indole derivatives with 2-(2-alkynyl)aryl cyclopropane-1,1-diesters (ACPs) have been developed. A series of tetracyclic indole derivatives were delivered in a 77% average yield with excellent regioselectivities enabled by Au(I)/Sc(III) bimetallic relay catalysis. A gram-scale reaction and further transformation of the resulting tetracyclic indoles demonstrated the practical utility of this protocol. Moreover, the photophysical properties of the obtained multicyclic compounds were also investigated.