Pd-Catalyzed Domino Reactions Involving Alkenes To Access Substituted Indole Derivatives

Abstract

Palladium-catalyzed domino reactions are advanced tools in achieving various nitrogen-containing heterocycles in an efficient and economical manner due to the reduced number of steps in the process. This review highlights recent advances in domino processes aimed at the synthesis of indole derivatives and polycyclic systems containing the indole nucleus in intra/intra- or intra/intermolecular reactions. In particular, we consider domino processes that involve a double bond in a step of the sequence, which allow the issue of regioselectivity in the cyclization to be faced and overcome. The different sections in this review focus on the synthesis of the indole nucleus and functionalization of the scaffold starting from different substrates that have been identified as activated starting materials, which involve a halogenated moiety or unactivated unsaturated systems. In the former case, the reaction is under Pd(0) catalysis, and in the second case a Pd(II) catalytic species is required and then an oxidant is necessary to reconvert the Pd(0) into the active Pd(II) species. On the other hand, the second method has the advantage that it uses easy available and inexpensive substrates.1 Introduction2 Indole Scaffold Synthesis2.1 Activated Substrates2.2 Unactivated Substrates3 Functionalization of Indole Scaffold3.1 Activated Substrates3.2 Unactivated Substrates4 Conclusions

Asymmetric Pd(II)‐Catalyzed C−O, C−N, C−C Bond Formation Using Alkenes as Substrates: Insight into Recent Enantioselective Developments

“…The formation of two carbon−heteroatom bonds across an unsaturated system in one‐pot process with full control of selectivity (regio‐, diastereo‐, and enantioselectivity), is challenging as well as extremely desired in organic chemistry. The generation of molecular complexity, as functionalized heterocycles and functionalized aliphatic chains in rapid manner from simple alkene precursors [39–44] requires fine‐tuning of reaction conditions. Some years ago the possibility to add functional groups at the desired site in a regio‐, diastereo‐ and enantioselective manner was an ideal scenario, but the recent developments have shown that some limits can be exceeded [45] …”

Recent Progress in Gold‐Catalyzed Reactions of Alkynes for the Construction of Indole Frameworks

“…Various other methodologies including transition-metal-catalyzed protocols have also been developed to access this structural motif. [51][52][53][54][55][56] On the other hand, gold-catalyzed organic transformations are emerging as a powerful tool during the past decade for the construction of diverse heterocyclic frameworks. [57][58] The fundamental mode of gold-catalyzed organic reactions is the activation of carbon-carbon multiple bonds, mostly alkyne, to facilitate the attack of a nucleophile under mild conditions.…”

Indole frameworks via transition-metal-free annulation: a current perspective

“…The recently published reviews mainly focussed on the transition-metalcatalyzed synthetic approaches towards the indole skeleton. [46][47][48][49][50][51][52][53][54][55][56] In 2018, Cheng and Shao published an interesting review on organocatalytic asymmetric transformations involving the cyclic imine moiety in indole analogues. 57 Immediately after, Neto and Zeni published a review article on metalfree synthesis of indoles from typical alkynes and a nitrogen source.…”