Reaction between glutaric anhydride and N-benzylidenebenzylamine, and further transformations to new substituted piperidin-2-ones

The Castagnoli–Cushman Reaction

Since the first reports of the reaction of imines and cyclic anhydrides by Castagnoli and Cushman, this procedure has been applied to the synthesis of a variety of lactams, some of them with important synthetic or biological interest. The scope of the reaction has been extended to the use of various Schiff bases and anhydrides as well as to different types of precursors for these reagents. In recent years, important advances have been made in understanding the mechanism of the reaction, which has historically been quite controversial. This has helped to develop reaction conditions that lead to pure diastereomers and even homochiral products. In addition, these mechanistic studies have also led to the development of new multicomponent versions of the Castagnoli–Cushman reaction that allow products with more diverse and complex molecular structures to be easily obtained.

Synthesis of Novel 1-Oxo-2,3,4-trisubstituted Tetrahydroisoquinoline Derivatives, Bearing Other Heterocyclic Moieties and Comparative Preliminary Study of Anti-Coronavirus Activity of Selected Compounds

A series of novel 1-oxo-2,3,4-trisubstituted tetrahydroisoquinoline (THIQ) derivatives bearing other heterocyclic moieties in their structure were synthesized based on the reaction between homophthalic anhydride and imines. Initial studies were carried out to establish the anti-coronavirus activity of some of the newly obtained THIQ-derivatives against two strains of human coronavirus-229E and OC-43. Their antiviral activity was compared with that of their close analogues, piperidinones and thiomorpholinones, previously synthesized in our group, with aim to expand the range of the tested representative sample and to obtain valuable preliminary information about biological properties of a wider variety of compounds.

Trifluoroethanol Promoted Castagnoli-Cushman Cycloadditions of Imines with Homophthalic Anhydride

Lactams are essential compounds in medicinal chemistry and key intermediates in the synthesis of natural products. The Castagnoli–Cushman reaction (CCR) of homophthalic anhydride with imines is an exciting method for accessing cyclic densely substituted lactam products. Most CCRs need to be catalyzed or heated. Herein, we report a new, efficient, metal and catalyst-free CCR for the synthesis of poly-substituted 3,4-lactams utilizing the unique properties of trifluoroethanol (TFE). This procedure provides high-speed and smooth access to a broad range of densely substituted 3,4-lactams in good yields and a 100% atom-economical fashion.

One-step route to tricyclic fused 1,2,3,4-tetrahydroisoquinoline systems via the Castagnoli-Cushman protocol

The Castagnoli-Cushman reaction of 3,4-dihydroisoquinolines with glutaric anhydride, its oxygen and sulfur analogues was investigated as a one-step approach to the benzo[a]quinolizidine system and its heterocyclic analogs. An extension towards the pyrrolo[2,1-a]isoquinoline system was achieved with the use of succinic anhydride. The results are evidence of an unexplored method for the access of the aforementioned tricyclic annelated systems incorporating a bridgehead nitrogen atom. The structures and relative configurations of the new compounds were established by means of 1D and 2D NMR techniques. The reactions between 1-methyldihydroisoquinoline and glutaric, diglycolic and succinic anhydrides yielded unexpected isoquinoline derivatives containing an exocyclic double bond. The compounds prepared bear the potential to become building blocks for future synthetic bioactive molecules.

Toward lead-oriented synthesis: one-pot version of Castagnoli condensation with nonactivated alicyclic anhydrides

One-pot variation of Castagnoli condensation, that is, reaction of cyclic anhydrides, amines, and aldehydes, has been developed as a combinatorial approach to 1,2-disubstituted 5-oxopyrrolidine- and 6-oxopiperidine-3-carboxylic acids, as well as their benzo-analogues. Utility of the method to multigram preparation of building blocks and synthetic intermediates was also demonstrated. The final products are obtained in high yields and diastereoselectivity. The method fits well in the concept of lead-oriented synthesis; in particular, it can be used for the design of lead-like compound libraries, even if the strictest cut-offs are applied to the physicochemical properties of their members.

(S)-Methyl 2-[(3R,4R)-2-benzyl-3-(2-fur-yl)-1-oxo-1,2,3,4-tetra-hydro-isoquinoline-4-carboxamido]-3-(1H-indol-3-yl)propanoate

The title compound, C(33)H(29)N(3)O(5), was synthesized by the reaction of racemic trans-2-benzyl-3-(2-fur-yl)-1-oxo-1,2,3,4-tetra-hydro-isoquinoline-4-carboxylic acid, l-tryptophan methyl ester and diisopropylcarbodiimide in dry dichloro-methane. The furan ring is disordered over two positions in a 0.859 (14):0.141 (14) ratio. In the 1,2,3,4-tetra-hydro-iso-quin-oline ring system, the heterocyclic ring is not planar, with puckering parameters Q(T) = 0.448 (2) Å, θ = 64.9 (3) and ϕ = 268.3 (3)°. The crystal is extended into a three-dimensional supra-molecular architecture through inter-molecular N-H⋯O hydrogen bonds and C-H⋯π inter-actions. The absolute structure was assigned by reference to the chiral starting material.

Methyl trans-(±)-1-oxo-2-phenethyl-3-(thio-phen-2-yl)-1,2,3,4-tetra-hydro-isoquinoline-4-carboxyl-ate

In the title compound, C(23)H(21)NO(3)S, the piperidine ring of the tetra-hydro-isoquinolinone unit adopts a screw-boat conformation. The thio-phene ring is disordered in a 0.700 (3):0.300 (3) ratio by an approximate 180° rotation of the ring around the C-C bond linking the ring to the tetra-hydro-isoquinolinone unit. The benzene ring of the tetra-hydro-isoquinolinone unit makes dihedral angles of 83.1 (2) and 62.38 (11)° with the major occupancy thio-phene ring and the phenyl ring, respectively. The dihedral angle between the phenyl ring and the thio-phene ring is 71.0 (2)°. In the crystal structure, mol-ecules are linked together by inter-molecular C-H⋯O and C-H⋯π inter-actions.