Gold-Catalyzed Cycloisomerization of 1,6-Diyne Carbonates and Esters to 2,4a-Dihydro-1H-fluorenes

Abstract

A synthetic method to prepare 2,4a-dihydro-1H-fluorenes efficiently from gold(I)-catalyzed 1,2-acyloxy migration/cyclopropenation/Nazarov cyclization of 1,6-diyne carbonates and esters is described. The suggested reaction pathway provides rare examples of [2,3]-sigmatropic rearrangement in this class of compounds as well as the involvement of an in situ formed cyclopropene intermediate in gold catalysis. Experimental and ONIOM(QM:QM') [our own n-layered integrated molecular orbital and molecular mechanics(quantum mechanics:quantum mechanics')] computational studies based on the proposed Au carbenoid species provide insight into this unique selectivity.

Gold‐Catalyzed Intramolecular Cyclizations of Cyclopropenes with Propargylic Esters

“…[1] In the presence of gold catalysts, propargylic esters readilyu ndergo 1,2-or 1,3-acyloxy migration, resulting in different cascade reactions. [2] Indeed, many groups includingo urs have made numerousc ontributions in this research area. [3] On the otherh and, cyclopropenes are highly strained but readily prepared compounds that can serve as useful building blocks in organic synthesis.…”

Gold-Catalysed Oxidative Cycloisomerisation of 1,6-Diyne Acetates to 1-Naphthyl Ketones

“…[18,30] An example of this is the gold(I)-catalysed preparation of 2,4a-dihydro-1H-fluorenes from 1,6-diyne esters in which computational studies revealed the likely involvement of the cyclopropene adduct I and gold carbenoid species II (Scheme 1a). [28] Closely following this work, the participation of these type of intermediates was proposed in the cycloisomerisation of 1,6-diyne esters to vinyl-substituted b-napthols (Scheme 1b). [29] Building on these initial studies, we were drawn to the potential reactivity of aryl-substituted 1,6-diyne esters containing a benzene tether (Scheme 1c).…”

Neue Ansätze für die Synthese von Metallcarbenen

“…Eine Cyclopropenierung ergab dann die Cyclopropene 341 , die über eine Ringöffnung zu den zweiten Au‐Carbenen 342 umgewandelt wurden, die mit dem Goldcarbokation 343 in Resonanz stehen. Eine Nazarov‐Cyclisierung von 343 lieferte die Endprodukte 338 (Schema a) . Ein auf analoge Weise gebildete Goldcarben 350 kann außerdem mit zwei Molekülen des Aldehyds 345 in einer [2+2+1]‐Cycloaddition zu den Produkten 346 reagieren (Schema b) …”