Acylation of Alkylidenecyclopropanes for the Facile Synthesis of α,β-Unsaturated Ketone and Benzofulvene Derivatives with High Stereoselectivity

Visible-light-promoted divergent functionalizations of methylenecyclopropanes

Visible-light-induced monofunctionalization and difunctionalization of MCPs via ring-opening and cyclization processes have been developed for the syntheses of difluoromethyl compounds, alkyl compounds, halides, and sulfonyl compounds.

[C^N]-Alkenyl Gold(III) Complexes by Proximal Ring-Opening of (2-Pyridyl)alkylidenecyclopropanes: Mechanistic Insights

Pyridine-substituted alkylidenecyclopropanes (Py-ACPs) react with gold(III) salts under mild reaction conditions through an unprecedented, proximal ring-opening pathway, to generate highly appealing, catalytically active pyridine alkenyl [C^N]-gold(III) species. Mechanistic studies reveal that the activation of the C-C bond of the ACP takes place through an unusual concerted, σ-bond metathesis type-process.

Thermally-induced intramolecular [2 + 2] cycloaddition of acrylamide-tethered alkylidenecyclopropanes

An efficient and highly regio- and diastereoselective synthetic method to cyclobutane-containing spiro[2.3]hexane fused with six-membered hetero-cycles has been disclosed via a thermally-induced intramolecular [2 + 2] cycloaddition of acrylamide-tethered alkylidenecyclopropanes. The DFT calculations indicate that this intramolecular cycloaddition proceeds in a concerted manner and account for the product selectivity. These reactions exhibited excellent yields and functional group tolerance under metal free conditions.

Synthesis of 1,2,4-Trisubstituted-(1H)-imidazoles through Cu(OTf)2-/I2-Catalyzed C-C Bond Cleavage of Chalcones and Benzylamines

1,2,4-Trisubstituted-(1H)-imidazoles have been synthesized by the Cu(OTf)₂- and I₂-catalyzed unusual C-C bond cleavage of chalcones and benzylamines. After the α,β-unsaturated C-C bond cleavage, the β-portion is eliminated from the reaction. Various aryl- and heteroaryl-substituted chalcones and benzylamines were well tolerated in this unusual transformation to yield the trisubstituted-(1H)-imidazoles.

Iron-catalyzed aerobic oxidation of allylic alcohols: the issue of C═C bond isomerization

An aerobic oxidation of allylic alcohols using Fe(NO3)3·9H2O/TEMPO/NaCl as catalysts under atmospheric pressure of oxygen at room temperature was developed. This eco-friendly and mild protocol provides a convenient pathway to the synthesis of stereodefined α,β-unsaturated enals or enones with the retention of the C-C double-bond configuration.

Rapid generation of molecular complexity in the Lewis or Brønsted acid-mediated reactions of methylenecyclopropanes

Although they are highly strained, methylenecyclopropanes (MCPs) are readily accessible molecules that have served as useful building blocks in organic synthesis. MCPs can undergo a variety of ring-opening reactions because the release of cyclopropyl ring strain (40 kcal/mol) can provide a thermodynamic driving force for reactions and the π-character of the bonds within the cyclopropane can afford the kinetic opportunity to initiate the ring-opening. Since the 1970s, the chemistry of MCPs has been widely explored in the presence of transition metal catalysts, but less attention had been paid to the Lewis or Brønsted acid mediated chemistry of MCPs. During the past decade, significant developments have also been made in the Lewis or Brønsted acid mediated reactions of MCPs. This Account describes chemistry developed in our laboratory and by other researchers. Lewis and Brønsted acids can be used as catalysts or reagents in the reactions of MCPs with a variety of substrates, and substituents on the terminal methylene or on the cyclopropyl ring of MCPs significantly affect the reaction pathways. During the past decade, we and other researchers have found interesting transformations based on this chemistry. These new reactions include the ring expansion of MCPs, cycloaddition reactions of MCPs with aldehydes and imines, cycloaddition reactions of MCPs with nitriles in the presence of strong Brønsted acid, radical reactions of MCPs with 1,3-dicarbonyl compounds, intramolecular Friedel-Crafts reactions of MCPs with arenes, acylation reactions of MCPs, and the reaction of MCPs with 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers. These Lewis or Brønsted acid mediated reactions of MCPs can produce a variety of new compounds such as cyclobutanones, indenes, tetrahydrofurans, and tetrahydroquinolines. Finally, we have also carried out computational studies to explain the mechanism of the Brønsted acid mediated reactions of MCPs with acetonitrile.

Stereospecific synthesis of alkylidenecyclopropanes via sequential cyclopropene carbomagnesation/1,3-carbon shift

Alkylidenecyclopropanes can be synthesized from enantiomerically enriched cyclopropene derivatives with >99% stereotransfer and good to excellent yield. The protocol comprises the stereoselective reaction of Grignard reagents with 1-alkoxymethyl-3-hydroxymethylcyclopropenes and a stereospecific [1,3] carbon shift reaction.