Brønsted Acid Mediated Cascade Reaction To Access 3-(2-Bromoethyl)benzofurans

Brønsted acid catalyzed Ficini [2 + 2] cycloaddition of ynamides with enones

Herein, we describe a novel metal-free Brønsted acid-catalyzed Ficini [2 + 2] cycloaddition of ynamides with enones under mild reaction conditions, leading to the formation of various cyclobutenamides in generally good to excellent yields within short reaction times. This work represents the first example of ynamides involved in a nonmetal-catalyzed [2 + 2] cycloaddition with enones.

Synthesis of 1,4-ketoaldehydes and 1,4-diketones by Mo-catalyzed oxidative cleavage of cyclobutane-1,2-diols

A new two-step procedure for the synthesis of 1,4-dicarbonyls has been developed involving an efficient and clean Mo-catalyzed oxidative cleavage of cyclobutane-1,2-diols with DMSO, which is used as solvent and oxidant. The required starting glycols were prepared by nucleophilic additions of organolithiums and Grignard reagents to easily available 2-hydroxycyclobutanones.

Stereoselective Synthesis of trans-Decalin-Based Spirocarbocycles via Photocyclization of 1,2-Diketones

Diastereoselective synthesis of the trans-decalin-based α-hydroxyl butanone spirocarbocycles bearing all-carbon quaternary stereogenic centers has been achieved via Norrish-Yang photocyclization of trans-decalin-substituted-2,3-butanediones using daylight. Density functional theory (DFT) calculations suggest that this diastereoselective reaction is affected by both substrate conformation and intramolecular hydrogen bonds. The developed chemistry could be applied to synthesizing the derivatives of the trans-decalin-based biologically important natural products.

Lithiated three-membered heterocycles as chiral nucleophiles in the enantioselective synthesis of 1-oxaspiro[2,3]hexanes

The reaction between configurably stable α-lithiated oxiranes and 3-substituted cyclobutanones allows obtaining enantiomerically enriched cyclobutanols (er > 98 : 2). These adducts, subjected to base-mediated Payne rearrangement, lead to the synthesis of a new class of oxaspirohexanes, useful precursors of 2,4-disubstituted cyclopentanones.

Visible light promoted continuous flow photocyclization of 1,2-diketones

The continuous flow Norrish-Yang photocyclization of 1,2-diketones has been developed and used for the synthesis of a large number of functionalized 2-hydroxycyclobutanones, under blue light irradiation and employing acetone as a solvent. This eco-friendly procedure represents a valid alternative to the reactions carried out in batches thus reducing the reaction times, the formation of secondary products and simplifying the purification steps. The use of differently substituted diketone compounds has allowed us to obtain a wide range of 2 and 3-functionalized cyclobutanones, thus allowing the evaluation of the scope and limitations of this procedure.

Last Decade of Unconventional Methodologies for the Synthesis of Substituted Benzofurans

This review describes the progress of the last decade on the synthesis of substituted benzofurans, which are useful scaffolds for the synthesis of numerous natural products and pharmaceuticals. In particular, new intramolecular and intermolecular C-C and/or C-O bond-forming processes, with transition-metal catalysis or metal-free are summarized. (1) Introduction. (2) Ring generation via intramolecular cyclization. (2.1) C7a-O bond formation: (route a). (2.2) O-C2 bond formation: (route b). (2.3) C2-C3 bond formation: (route c). (2.4) C3-C3a bond formation: (route d). (3) Ring generation via intermolecular cyclization. (3.1) C7a-O and C3-C3a bond formation (route a + d). (3.2) O-C2 and C2-C3 bond formation: (route b + c). (3.3) O-C2 and C3-C3a bond formation: (route b + d). (4) Benzannulation. (5) Conclusion.

Deconstructive Reorganization: De Novo Synthesis of Hydroxylated Benzofuran

An unprecedented deconstructive reorganization strategy for the de novo synthesis of hydroxylated benzofurans from kojic acid- or maltol-derived alkynes is reported. In this reaction, both the benzene and furan rings were simultaneously constructed, whereas the pyrone moiety of the kojic acid or maltol was deconstructed and then reorganized into the benzene ring as a six-carbon component. Through this strategy, at least one free hydroxyl group was introduced into the benzene ring in a substitution-pattern tunable fashion without protection-deprotection and redox adjustment. With this method, a large number of hydroxylated benzofuran derivatives with different substitution-patterns have been prepared efficiently. This methodology has also been shown as the key step in a collective total synthesis of hydroxylated benzofuran-containing natural products (11 examples).

Metal and Oxidant-Free Brønsted Acid-Mediated Cascade Reaction to Substituted Benzofurans

Substituted hydroxy-benzofurans are easily accessible by treatment of resorcinols and 1,2-diaza-1,3-dienes (DDs) under acidic conditions. The reaction happens through an uncommon Michael reaction between aromatic derivatives as aromatic C(sp²)-H nucleophiles and DDs as acceptors. Also, the behavior of different phenols and 2-naphthol was investigated.