Development of an Alkyne Analogue of the de Mayo Reaction: Synthesis of Medium‐Sized Carbacycles and Cyclohepta[b]indoles

Abstract

Embedded medium-sized carbacycles and cyclohepta [b]indoles occur frequently as scaffold elements in natural products and bioactive compounds.Described herein is ac onceptionally novel photochemically triggered cascade process to these scaffolds.K ey to the cascading ring-expansion process is an unprecedented intramolecular alkyne analogue of the de Mayor eaction. Prof. Dr.J.Rehbein FakultätfürChemie und Pharmazie, UniversitätRegensburg 93053 Regensburg (Germany) Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Development of an Alkyne Analogue of the de Mayo Reaction: Synthesis of Medium‐Sized Carbacycles and Cyclohepta[b]indoles

“…This second-generation linker (X = Y = O) should be amenable to straightforward linker cleavage using either Brønsted-or Lewis-acidic conditions. [15] In contrast, irradiation of 6b resulted in the formation of 7b in only 53 %y ield along with some decomposition. [17,18] Aiming to establish am etal-free single-step annulative access to these scaffolds, we studied the photochemistry of 6a-f (Table 3).…”

Stereoselective Synthesis of Cyclohepta[b]indoles by Visible‐Light‐Induced [2+2]‐Cycloaddition/retro‐Mannich‐type Reactions

“…It shows that although the fluorescence of FCNIrpic could be quenched by enaminone 20 , no reaction occurred when 20 was irradiated with blue LEDs in the presence of FCNIrpic. Conversely, when we irradiated enaminone 20 with a high‐pressure Hg lamp in the absence of FCNIrpic, the annulation product 21 was obtained in 77 % yield, indicating that once triplet state 20* is formed, it should undergo [2+2]/retro‐Mannich‐type process [4a, 14j] . Thus, single electron oxidation ( 20→20 ⋅+ ) is a more plausible explanation for the non‐productive luminescence‐quenching.…”

An Update on Cyclohepta[b]indoles

“…[40] In 2018, Tymann et al made an initial report on a photochemical synthesis of the cyclohepta[b]indole scaffold. [41] Originally designed for tropolone synthesis is the context of terpenoide total synthesis, [42] the photochemically triggered two-carbon ring expansion was adapted and expanded for cyclohepta 32). [43] The two-carbon ring-expansion exploits the inherent atom economy of a photochemically triggered cycloisomerization.…”