Acyliminium ion cyclizations: Synthesis of thieno[2′,3′:3,4]pyrrolo[2,1-a] isoindolone and benzo[a]thieno[2,3(3,2 or 3,4)-g]indolizinones

Hybrid Heterocycles: Ag(I)-Catalyzed C-C/C-N/C-O Coupled Cascade Dual Cyclization to Valuable Indolo-4H-indolones and Indolo-4H-chromenes

Herein, we report a highly efficient Ag(I)-catalyzed indolyzation with Friedel-Crafts alkylation through a cascade cyclization strategy for accessing valuable hybrid heterocycles for the first time. This general strategy consists of forming four C-C/C-N/C-O bonds toward dual annulation reactions of 2-alkynylanilines with methyl benzoate-2-carboxaldehydes and aromatic amines, as well as with salicylaldehydes and malononitrile. Variably substituted new indolo-4H-phthalimidines and indolo-4H-chromenes were synthesized with excellent yields (85-93%) under mild reaction conditions.

α-Hydroxylactams as Efficient Entries to Diversely Functionalized Ferrociphenols: Synthesis and Antiproliferative Activity Studies

The [ferrocene-ene-phenol] motif has been identified as the pharmacophore responsible for the anticancer activity of the family of ferrocene-based molecules coined ferrocifens, owing to its unique redox properties. The addition of imide entities to the historical ferrociphenol scaffold tremendously enhanced the cytotoxic activity of a large panel of cancer cell cultures and preliminary studies showed that the reduction of one of the carbonyl groups of the imide groups to the corresponding α-hydroxylactams only slightly affected the antiproliferative activity. As a continuation to these studies, we took advantage of the facile conversion of α-hydroxylactams to highly electrophilic N-acyliminium ions to graft various substituents to the imide motif of phthalimido ferrocidiphenol. Cell viability studies showed that the newly synthesized compounds showed diverse cytotoxic activities on two breast cancer cell lines, while only one compound was significantly less active on the non-tumorigenic cell line hTERT-RPE1.

Access to 3-spiroindolizines containing an isoindole ring through intra-molecular arylation of spiro-N-acyliminium species: a new family of potent farnesyltransferase inhibitors

Based on N-acyliminium species, two efficient and rapid approaches to diversify spirocyclic systems connected by two different carbon centers to the isoindole ring have been developed. The imide reduction and the tandem oxidative cleavage of olefin/formyl-amide equilibration were at first selected as the key steps for these strategies. Ultimately the intramolecular α-amidoalkylation reaction was achieved through the arylation of α-acetoxy lactams or α-hydroxy lactams using, respectively, a Lewis acid or a Brønsted acid depending on the nature of N-acyliminium precursors. The latter led, in addition to the spiro-6-membered aza-heterocycles, to the formation of scarce spiro-5-membered analogues which show promising inhibitory activities on human farnesyltransferase in the nanomolar range demonstrating improved IC50 values of up to 1.5 nM.

Synthesis of tricyclic 3-hydroxyisoindolin-1-ones via triethylamine-catalyzed domino reactions of electron-deficient alkynes with phthalimidomalonate derivatives

A triethylamine-catalyzed domino reaction between phthalimidomalonate derivatives and activated alkynes has been developed under mild conditions.

Synthesis of Functionalized Isoindolinones: Addition of In Situ Generated Organoalanes to Acyliminium Ions

Addition of in situ generated di- or trisubstituted alkenylalanes to N-acyliminium ions provides rapid access to functionalized isoindolinones. Subsequent ring closing metathesis leads to tricyclic products. These transformations proceed under mild conditions and allow for the convergent synthesis of biologically significant scaffolds from readily available starting materials.

Solid-phase intramolecular N-acyliminium Pictet-Spengler reactions as crossroads to scaffold diversity

A novel solid-phase intramolecular Pictet-Spengler reaction is presented. The approach utilizes masked aldehyde building blocks protected as their N-Boc-1,3-oxazinanes for the clean generation of solid-supported aldehydes. When exposed to simple acidic treatment, the aldehyde functionality is rapidly released and becomes susceptible to nucleophilic attack from an amide nitrogen of the peptide backbone, which results in the formation of a highly reactive cyclic N-acyliminium ion. Subsequently, a quantitative and highly stereoselective Pictet-Spengler reaction takes place by attack of the indole from a neighboring tryptophan, thus appending two new N-fused rings to the indole moiety. Extension of this intramolecular reaction to substituted indoles, and other reactive heterocycles, such as furane and thiophenes, provides a convenient and rapid access to a range of pharmacologically interesting tri- and tetracyclic scaffolds. Finally, the reaction products may conveniently be released from the solid support (PEGA) by cleavage of the base-labile linker (HMBA).

Stereoselective tetrapyrido[2,1-a]isoindolone synthesis via carbanionic and radical intermediates: a model study for the Tacaman alkaloid D/E ring fusion

Cyclization under both radical and carbanionic conditions of N-substituted 3-phenylsulfanylisoindolin-1-one 14 containing a chiral N-tether incorporating an enoate ester as the acceptor leads to tetrahydropyrido[2,1-a]isoindolones stereoselectively. The major product 17 from carbanionic cyclization was stereoselectively desulfurized with nickel boride allowing correlation of cyclization products from both methodologies. The cyclization stereoselectivities have been rationalised using a transition-state model in which the acceptor grouping adopts a pseudoaxial configuration. This contrasts with other 6-exo-trig processes in which a pseudoequatorial configuration is normally adopted, and has been attributed to the steric influence imposed by the bulky tert-butyldiphenylsilyloxy chiral auxiliary allylic to the enoate ester. The product stereochemistries provide models for the required cis-stereochemistry of the D/E ring fusion of the Tacaman alkaloid skeleton via the relatively unexplored C-3-C-14 bond disconnection.