Enantioselective synthesis of functionalized 2-amino-4H-chromenes via the o-quinone methides generated from 2-(1-tosylalkyl)phenols

Pd-catalyzed asymmetric etherification of 2H-chromenes: enantioselective construction of chiral 4-alkoxy-4H-chromenes

A new strategy for the construction of a chiral 4-alkoxy-4H-chromene skeleton was reported. A series of chiral 4-alkoxy-4H-chromenes containing the trifluoromethyl group were obtained in good yields (up to 80% yield) and excellent enantioselectivity (up to 93% ee).

Brønsted Acid Catalyzed Friedel-Crafts Alkylation of Naphthols with In Situ Generated Naphthol-Derived ortho-Quinone Methides: Synthesis of Chiral and Achiral Xanthene Derivatives

We disclose herein an enantioselective protocol for the Brønsted acid catalyzed addition of naphthols to in situ generated naphthol-derived ortho-quinone methides (o-QMs) followed by intramolecular cyclization, which delivers substituted chiral xanthene derivatives, in a one-pot reaction sequence under mild conditions. This process serves to convert naphthol-derived ortho-hydroxyl benzylic alcohols into reactive naphthol-derived o-QMs using a chiral phosphoric acid (CPA) catalyst. Moreover, it is helpful in controlling the enantioselectivity of the carbon-carbon bond-forming event via hydrogen-bonding followed by intramolecular cyclization. Additionally, for the first time, we observe a Brønsted acid catalyzed C(sp²)-C(sp³) bond cleavage of naphthol-derived ortho-hydroxyl benzylic alcohols for the synthesis of achiral xanthene (sigma plane containing) derivatives in good to excellent yields.

N-Heterocyclic carbene-catalysed homoenolate addition reaction to 3-cyano-2-imino-2H-chromenes: synthesis of C4-functionalized 2-amino-3-cyano-4H-chromene

A NHC-catalyzed homoenolate addition reaction between enals and iminochromenes to yields of a new type of C4-functionalized 2-amino-4H-chromenes has been developed.

Development of potential anticancer agents and apoptotic inducers based on 4-aryl-4H chromene scaffold: Design, synthesis, biological evaluation and insight on their proliferation inhibition mechanism

An array of 4-aryl-2-amino-4H chromene derivatives were designed, synthesized, and evaluated for cytotoxic activity against four cancer cell lines and two non-cancerous cell lines. The most active candidates were further screened for their in vitro anticancer activity on NCI panel of 60 human cancer cell lines where compounds 2a, 2b, 4a-2, and 2e showed promising activity against various leukemia, non-small lung, renal, prostate, and breast cancer cell lines, particularly against NCI-H522 non-small lung cancer cell line (GI₅₀ of 0.35-0.60 µM), MCF7 breast cancer cell line (GI₅₀ of 0.34-0.59 µM), and MDA-MB-468 breast cancer cell line (GI₅₀ of 0.23-0.40 µM). Compound 2b was the most potent against all leukemia and prostate cancer cell lines with GI₅₀ values (0.29-0.60 µM). Compound 2b inhibited the proliferation of MCF-7 and HepG2 cells by inducing cell cycle arrest and apopotosis. 2b downregulated the mRNA abundance of BAX, Apaf-1 and caspase-3 and upregulated BCL-2. The activities of caspase-3 and caspase-9 were declined in MCF-7 and HepG2 cells treated with compound 2b. Compounds 2b and 4a-2 inhibited tubulin polymerization, with an IC₅₀ values of 0.92 and 1.13 µM, respectively. These findings indicate that these synthesized compounds may represent potential drug candidates to inhibit the proliferation of different types of cancer cells.

A rhodium-catalysed conjugate addition/cyclization cascade for the asymmetric synthesis of 2-amino-4H-chromenes

The enantioselective synthesis of 2-amino-4H-chromenes via the cascade rhodium-catalysed conjugate addition/hetero Thorpe-Ziegler reaction is reported. Moderate to good yields (up to 98%) and high enantioselectivities (up to 92% ee) were obtained with a chiral diene-coordinated rhodium complex as the catalyst. This protocol remedies the methodological deficiency in the asymmetric synthesis of 4-aryl 2-amino-4H-chromenes.

Divergent Asymmetric Reactions of ortho-Quinone Methides with α-Thiocyanato Indanones for the Synthesis of Spiro- and Fused-Indanones

Reported in this work is a water triggered chemo-divergent enantioselective spiro-annulation and cascade reaction of ortho-quinone methides (o-QMs) with α-thiocyanato indanones catalyzed by a chiral organic base. In the case of spiro-annulation, the use of trace amount of water as additive is critical to achieve high enantioselectivity (up to 96 % ee). We found that a cascade reaction was enabled by just tuning the ratio of water in solvent. Accordingly, two new highly efficient asymmetric reactions for the divergent synthesis of spiro- and fused-indanone scaffolds with excellent enantioselectivities (up to 99 % ee) were developed. Mechanistic investigations suggest that interfacial hydrogen bonding may play an important role in achieving the switchable reaction pathways.

Diastereoselective synthesis of CF3-dihydrobenzofurans by [4+1] annulation of in situ-generated CF3-o-quinone methides and sulfur ylides

An efficient and highly diastereoselective synthesis of CF₃-dihydrobenzofurans by the reaction of in situ-generated CF₃-oQMs in the presence of a base with sulphur ylides is put forward. The generality of the present developed method was well studied with diverse substrates to access the corresponding products in excellent yields. The highly reactive CF₃-oQM has been utilized first time for the annulation reaction.

The first [4 + 1] annulation reaction of in situ-generated highly electrophilic CF₃-ortho-quinone methides with sulphur ylides has been put forth under mild reaction conditions to access CF₃-dihydrobenzofurans.

Organocatalytic asymmetric addition of thioglycolates to o-quinone methides: a route to 5-substituted-5H-benzoxathiepine-2(3H)-ones

Herein we have developed the first enantioselective synthesis of 5-substituted-5H-benzoxathiepine-2(3H)-ones. 2-Sulfonylmethyl phenols and thioglycolates were employed as reaction partners in this method. The desired thia Michael products were obtained via bifunctional squaramide catalyzed conjugate addition reaction to in situ generated o-quinone methides and then basic hydrolysis followed by cyclization led to the formation of 5-substituted-5H-benzoxathiepine-2(3H)-ones. Broad scope and moderate to high enantioselectivities were observed for both products.

Synthesis and pharmacological properties of polysubstituted 2-amino-4H-pyran-3-carbonitrile derivatives

2-Amino-3-cyano-4H-chromenes are structural core motifs that received increasing attention in the last years due to their interesting potential pharmacological properties. In this review, the synthetic methods for these compounds are classified based on the type of catalyst in the pertinent reactions. In addition, the wide range of pharmacological properties of these compounds is covered in a separate section.

An organic-base catalyzed asymmetric 1,4-addition of tritylthiol to in situ generated aza-o-quinone methides at the H2O/DCM interface

Highly enantioselective organocatalytic Michael addition of tritylthiol to N-o-QM intermediates generated in situ at the H₂O/DCM interface is presented.

Straightforward Synthesis of Bifunctional Phosphorus Phenols via Phosphination of In Situ Generated o-Quinone Methides

An efficient and practical approach towards bifunctional phosphorus phenols has been developed through a reaction of diphenylphosphine oxide and the o-quinone methides in situ generated from 2-tosylalkyl phenols under basic conditions. This protocol features simple experimental procedures under mild conditions and is easily scaled up. With this method, a variety of diarylmethyl phosphine oxides can be produced with up to 92% yield.

Base-mediated diastereoselective [4 + 3] annulation of in situ generated ortho-quinone methides with C,N-cyclic azomethine imines

An efficient [4 + 3] annulation of 2-(1-tosylalkyl)phenols with C,N-cyclic azomethine imines via in situ generation of ortho-quinone methides (o-QMs) under mild basic reaction conditions is disclosed, furnishing biologically interesting seven-membered heterocyclic compounds with moderate to good yields and excellent diastereoselectivities. A gram-scale reaction is performed to demonstrate the potential in industrial application and two transition states are proposed to rationalize the outstanding diastereoselectivity.

Bifunctional squaramide-catalyzed synthesis of chiral dihydrocoumarins via ortho-quinone methides generated from 2-(1-tosylalkyl)phenols

A bifunctional squaramide-catalyzed reaction of azlactones with o-quinone methides in situ generated from 2-(1-tosylalkyl)-phenols has been successfully developed under basic conditions, providing an efficient and mild access to chiral dihydrocoumarins bearing adjacent tertiary and quaternary stereogenic centers in high yields with excellent diastereo- and enantioselectivities.

Recent advances in the application of Diels–Alder reactions involving o-quinodimethanes, aza-o-quinone methides and o-quinone methides in natural product total synthesis

This review summarizes recent advances in Diels–Alder reactions involving o-QDMs, o-QMs and aza-o-QMs. The power and potential of this strategy in organic synthesis and natural product total synthesis is highlighted.

Catalytic asymmetric 1,6-conjugate addition of in situ generated para-quinone methides with tritylthiol

An asymmetric phase-transfer catalyzed 1,6-conjugate addition of in situ generated para-quinone methides with tritylthiol has been developed.

Asymmetric Synthesis of 2,3-Dihydrobenzofurans by a [4+1] Annulation Between Ammonium Ylides and In Situ Generated o-Quinone Methides

A highly enantio‐ and diastereoselective [4+1] annulation between in situ generated ammonium ylides and o‐quinone methides for the synthesis of a variety of 2,3‐dihydrobenzofurans has been developed. The key factors controlling the reactivity and stereoselectivity were systematically investigated by experimental and computational means and the energy profiles obtained provide a deeper insight into the mechanistic details of this reaction.

Regioselective α-Addition of Deconjugated Butenolides: Enantioselective Synthesis of Dihydrocoumarins

The enantioselective α-addition of deconjugated butenolides has rarely been exploited, in contrast to the well-studied γ-addition of deconjugated butenolides. In this study, an unprecedented asymmetric α-addition/transesterification of deconjugated butenolides with ortho-quinone methides generated in situ afforded a series of functionalized 3,4-dihydrocoumarins containing two contiguous stereogenic centers with excellent diastereo- and enantioselectivity. DFT calculations suggested that the rarely observed regioselectivity was due to the distortion energy that resulted from the interaction between the nucleophilic dienolate and the electrophilic ortho-quinone methide.

Organocatalytic asymmetric conjugate addition of t-butyl nitroacetate to o-quinone methides: synthesis of optically active α-nitro-β,β-diaryl-propionates

α-Nitro-β,β-diaryl-propionates were prepared with good yields and excellent enantioselectivities via asymmetric conjugate addition of t-butyl nitroacetate to in situ generated o-quinone methides.

Enantioselective [4 + 1] cycloaddition of ortho-quinone methides and bromomalonates under phase-transfer catalysis

An enantioselective [4 + 1] cycloaddition reaction of ortho-quinone methides and bromomalonates using a quinine and BINOL derived phase-transfer catalyst is described.

Chiral phosphoric acid catalyzed enantioselective annulation of acyclic enecarbamates to in situ-generated ortho-quinone methides

The first organocatalytic asymmetric [4 + 2]-cycloaddition reaction between acyclic enecarbamates with in situ generated ortho-quinone methides has been developed using chiral phosphoric acids as catalysts.

Asymmetric synthesis of chromene skeletons via organocatalytic domino reactions of in situ generated ortho-quinone methide with malononitrile and β-functionalized ketone

Enantioselective organocatalytic domino reactions of in situ generated ortho-quinone methides with malononitrile and β-functionalized ketones have been developed. This strategy could generate various chiral chromenes in high yields and stereoselectivities.

Enantioselective synthesis of chiral α,β-unsaturated γ-substituted butyrolactams by organocatalyzed direct asymmetric vinylogous Michael addition of α,β-unsaturated γ-butyrolactam to 2-enoylpyridines

Approach providing a series of optically active α,β-unsaturated γ-substituted butyrolactams in high yields with excellent diastereo- and enantioselectivities.

Indium triflate catalyzed microwave-assisted alkenylation of methoxyphenols: synthesis of indenes and chromenes

In(OTf)3 catalyzed microwave-assisted alkenylation of methoxyphenols was investigated. Exclusive formation of either indenes or chromenes was observed depending on the position of the methoxy group on phenol. The structures of 1H-inden-4-ol derivatives (4a-e) and 4H-chromene derivatives (5a-j) were established by NMR ((1)H & (13)C) and high-resolution mass spectra, which were further supported by single crystal X-ray analysis of 4c and 5a.