Connect Four: Tetraarylated Dihydropentalenes and Triarylated Monocyclic Pentafulvenes from Cyclopentadienes and Enones

Abstract

In search of novel pentalenide ligands for use in organometallic chemistry and homogeneous catalysis, we report the scope of a straightforward base-promoted Michael annulation of cyclopentadienes with α,β-unsaturated ketones that allows the introduction of symmetrical as well as unsymmetrical aryl and alkyl substitution patterns including electron-donating as well as electron-withdrawing substituents. More than 16 examples of various isomers of 1,3,4,6-tetraarylated dihydropentalenes have been synthesized in isolated yields of up to 78%, representing a substantial expansion of the range of dihydropentalene scaffolds known to date. Double bond isomerization between the two pentacyclic rings in 1,2-dihydropentalenes with electronically different substituents occurred depending on the polarization of the molecule. The melting points of the air-stable dihydropentalenes decrease, and their solubilities in organic solvents improve with increasing substitution and decreasing symmetry of the molecule. A competitive pseudo-retro-aldol pathway produces 1,3,6-triarylated monocyclic pentafulvenes as side products in yields of 9−68%, which can be cleanly isolated (8 new examples) and used for other synthetic purposes, including separate cyclization to other dihydropentalenes.

Twinned versus linked organometallics - bimetallic “half-baguette” pentalenide complexes of Rh(i)

“…We have recently described the facile and modular syntheses of tetra-substituted dihydropentalenes 59 and introduced the first tetra-arylated pentalenide, M 2 [Ph 4 Pn] (M = Li, Na, K) 60 and the first alkaline earth pentalenide, Mg[Ph 4 Pn] . 61,62 The increased solubility and ease of separation of MgX 2 transmetalation by-products (through induced precipitation by addition of 1,4-dioxane 63,64 ) are key advantages of Mg[Ph 4 Pn] over M 2 [Ph 4 Pn] which make it a prime candidate to explore the coordination chemistry of Ph 4 Pn 2− by way of salt metathesis.…”

“…[55][56][57] However, auxiliary ligand exchange reactions of late d-block pentalenide complexes are unknown save for Manriquez and co-workers who reported that [Cp*Ru II (μ:η 5 :η 3 Pn)Rh I (COD)] will liberate COD to form [Cp*Ru II (μ:η 5 :η 3 Pn)Rh I (CO) 2 ] when exposed to a CO atmosphere. 58 We have recently described the facile and modular syntheses of tetra-substituted dihydropentalenes 59 and introduced the first tetra-arylated pentalenide, M 2 [Ph 4 Pn] (M = Li, Na, K) 60 and the first alkaline earth pentalenide, Mg[Ph 4 Pn]. 61,62 The increased solubility and ease of separation of MgX 2 transmetalation by-products (through induced precipitation by addition of 1,4-dioxane 63,64 ) are key advantages of Mg[Ph 4 Pn] over M 2 [Ph 4 Pn] which make it a prime candidate to explore the coordination chemistry of Ph 4 Pn 2− by way of salt metathesis.…”

The coming of age: Understanding and tuning the electronic structure of pentalenides

“…§ Remarks regarding the access of multisubstituted dihydropentalenes can be found in the corresponding literature. 8,22 https://doi.org/10.26434/chemrxiv-2023-z8jdq ORCID: https://orcid.org/0000-0002-7613-1838 Content not peer-reviewed by ChemRxiv. License: CC BY 4.0 4 Scheme 1: Substituted pentalenides reported to date (left) and contribution of the work reported here (right).…”

“…License: CC BY 4.0 dihydropentalenes with LiNEt2 in tetrahydrofuran (Scheme 2). 22 Indeed, their much improved solubilities allowed for full characterisation by multi-nuclear NMR spectroscopy as well as mass spectrometry. As was the case for 2, the 1 H and 13 C NMR spectra of 3 and 4 indicated D2h symmetry, and their 7 Li NMR chemical shifts between 0.7 and −3.8 ppm suggested solvent-separated ion pairs (SSIP) 23 in THF solution at room temperature.…”

Palladium-Catalyzed Synthesis of 3,6-Diaryl-1-silylfulvenes: A Promising Entry for Preparing 1,3,6-Triarylfulvenes Bearing Three Different Aryl Groups

“…One method involves the introduction of an exomethylene moiety to already existing cyclopentadienes. This is the conventional method, which involves condensation of aldehydes or ketones with cyclopentadienes in the presence of bases. − The other method involves constructing fulvene rings from acyclic starting materials, that is, transition-metal-catalyzed cyclizations for the synthesis of fulvene rings from haloalkenes with alkynes − or alkynyl esters with silyl acetylenes . Most of the above-mentioned reactions gave fulvenes bearing the same substituents, and the fulvenes lack diversity in substitution patterns and types of substituents.…”