Rapid Access to Hindered α-Amino Acid Derivatives and Benzodiazepin-3-ones from Aza-Oxyallyl Cations

Desymmetric [3+3] Cyclization of p-Quinamines for the Synthesis of 1,2,4-Oxadiazines and Hydroquinoxalines

General and efficient strategies for highly diastereoselective synthesis of divergent heterocyclic scaffolds through desymmetric [3+3] cycloaddition of p-quinamines with 1,3-dipole surrogates hydroximoyl halides and α-halohydroxamates have been developed. This synthetic protocol provided a variety of heterocyclic architectures containing 1,2,4-oxadiazine and hydroquinoxaline skeletons in good yields with a wide substrate scope.

Organocatalytic Asymmetric [4 + 2]-Cycloadditions of 2-Aminophenyl Enones with Isatin-Derived Ketimines: Diastereo- and Enantioselective Synthesis of Spirooxindole-Tetrahydroquinazolines

A novel method for the enantioselective synthesis of spiro N,N-heterocyclic oxindoles has been developed, employing asymmetric [4 + 2]-cycloadditions of 2-aminophenyl enones with isatin-derived ketimines. This method employs an organocatalytic approach, utilizing a bifunctional squaramide-based catalyst. It enables the precise synthesis of chiral spirooxindole-tetrahydroquinazolines with intricate structures, featuring chiral quaternary centers. This process achieves remarkable results, including high yields and exceptional levels of enantioselectivity and diastereoselectivity (up to 96% yield, 95% ee, and >20:1 dr).

[4+2]-Cycloaddition of 2-Aminophenyl Enones with Cyclic N-Sulfimines to Access Enantioenriched Ring-Fused Aminals

Ring-fused aminal is an interesting structural skeleton in biologically active and pharmaceutically relevant compounds. A novel and efficient method for synthesizing benzosulfamidate-fused tetrahydroquinazolines is described. By employing the [4+2]-cycloaddition of 2-aminophenyl enones with cyclic N-sulfimines in the presence of DMAP as a base, the desired benzosulfamidate-fused tetrahydroquinazolines were obtained in good yields with high diastereoselectivities. Furthermore, an organocatalytic asymmetric [4+2]-cycloaddition was successfully achieved using a squaramide-based catalyst, enabling the enantioselective synthesis of chiral ring-fused tetrahydroquinazolines with high yields and enantio- as well as diastereoselectivities (up to 89 % yield, 94 % ee, and >30 : 1 dr).

Organocatalytic Asymmetric [3 + 2]-Annulations of γ-Sulfonamido/γ-Hydroxy-α,β-Unsaturated Ketones with Cyclic N-Sulfimines: Synthesis of Chiral Polyheterotricyclic Imidazolidines and Oxazolidines

The first organocatalytic asymmetric [3 + 2]-annulation of γ-sulfonamido-α,β-unsaturated ketones with cyclic N-sulfimines has been developed, and enantioenriched functionalized polyheterotricyclic imidazolidines were obtained in good yields and with excellent enantioselectivities. This approach was also extended to the asymmetric [3 + 2]-annulation of γ-hydroxy-α,β-unsaturated ketones, affording enantioenriched polyheterotricyclic oxazolidines. In addition, base-catalyzed [3 + 2]-annulations of γ-sulfonamido/γ-hydroxy-α,β-unsaturated ketones with cyclic N-sulfimines were re-investigated under mild reaction conditions for the synthesis of racemic polyheterotricyclic imidazolidines and oxazolidines with excellent diastereoselectivities.

Access to Sterically Hindered Thioethers (α-Thioamides) Under Mild Conditions Using α-Halohydroxamates: Application toward 1,4-Benzothiazinones and 4,1-Benzothiazepinones

Herein, we report a new and highly efficient approach for synthesizing congested α-thioamides under mild reaction conditions (mild base, room temperature, and short duration) using α-halo hydroxamates as direct alkylating agents. The reaction works well with both (hetero)aryl and alkyl thiols, tolerating a broad functional group and diverse substrate scope, including benzeneselenol for selenoether construction. The strategy enables efficient synthesis of biologically relevant 1,4 benzothiazinone and 4,1-benzothiazepinone cores, along with various other functionalized sulfur-based scaffolds of biological importance.

Synthesis of spirocyclic oxazole derivatives from 2-arylidene cycloalkanones and α-halohydroxamates

Herein we disclose a facile route to spirocyclic oxazole derivatives via [3 + 2] cycloaddition reactions between 2-arylidene cycloalkanones and azaoxyallyl cations that formed in situ from α-halohydroxamates in the presence of base. This methodology was shown to lead to an efficient formation of a series of functionalized spirocyclic oxazole derivatives in good to excellent yields.

Catalyst-Controlled Regiodivergent Synthesis of α/β-Dipeptide Derivatives via N-Allylic Alkylation of O-Alkyl Hydroxamates with MBH Carbonates

A controllable and regiodivergent N-allylation reaction involving readily available O-alkyl hydroxamates derived from natural α-amino acids has been developed, allowing regiospecific access to α/β-dipeptides containing α-unsaturated β-amino acids moieties in moderate to good yields. The regioselectivity could be conveniently switched by alternation of the catalysts and solvents.

Modular and Stereoselective Approach to Highly Substituted Indole/Pyrrole-Fused Diazepanones

A one-pot synthetic method for indole/pyrrole-fused 1,4-diazepanone scaffolds has been developed. This method involves a sequential amide coupling/intramolecular aza-Michael addition of 1H-indole/pyrrole-2-carboxylic acids with Morita-Baylis-Hillman-derived allylamines. The readily available starting materials, good stereoselectivity, and gram-scale synthesis make this method valuable for the construction of highly substituted fused heterocycles containing the 1,4-diazepanone moiety.

Synthesis of Five-Membered Cyclic Guanidines via Cascade [3 + 2] Cycloaddition of α-Haloamides with Organo-cyanamides

The convenient preparation of N2-unprotected five-membered cyclic guanidines was achieved through a cascade [3 + 2] cycloaddition between organo-cyanamides and α-haloamides under mild conditions in good to excellent yields (up to 99%). The corresponding cyclic guanidines could be easily transformed into hydantoins via hydrolysis.

Synthesis of thiazolidin-4-ones from α-enolic dithioesters and α-halohydroxamates

A facile access to thiazolidin-4-ones from α-enolic dithioesters and α-halohydroxamates in situ derived active 1,3-dipolar aza-oxyallyl cations was achieved under mild conditions.