Synthesis of strained 1,2-diazetidines via [3 + 1] cycloaddition of C,N-cyclic azomethine imines with isocyanides and synthetic derivation

Strained diazetidines are assembled simply from 1,3-dipolar cycloaddition of isocyanides and C,N-cyclic azomethine imines, and their diversified transformations are presented.

Synthesis of C-Unsubstituted 1,2-Diazetidines and Their Ring-Opening Reactions via Selective N-N Bond Cleavage

C-Unsubstituted 1,2-diazetidines, a rarely studied type of four-membered heterocyclic compounds, were synthesized through an operationally simple intermolecular vicinal disubstitution reaction. 1,2-Diazetidine derivatives bearing various N-arylsulfonyl groups were readily accessed and studied by experimental and computed Raman spectra. The ring-opening reaction of the diazetidine was explored and resulted in the identification of a selective N-N bond cleavage with thiols as nucleophiles, which stereoselectively produced a new class of N-sulfenylimine derivatives with C-aminomethyl groups.

Synthesis of 4,5-Diazaspiro[2.3]hexanes and 1,2-Diazaspiro[3.3]heptanes as Hexahydropyridazine Analogues

4,5-Diazaspiro[2.3]hexanes are made by dihalocarbene addition across the exocyclic double bond of readily accessible 3-alkylidene-1,2-diazetidines. Using difluorocarbene, generated from TMSCF₃/NaI, these spirocycles were produced in yields up to 97% by stereospecific addition across the alkene. Lower yields (up to 64%) were observed using more reactive dichlorocarbene, due to competitive insertion of the carbene into the N-N bond. Larger 1,2-diazaspiro[3.3]heptanes are produced by [2 + 2] cycloaddition of 3-alkylidene-1,2-diazetidines with tetracyanoethylene (TCNE) in up to 99% yield.

Regio- and Stereocontrolled Synthesis of 3-Substituted 1,2-Diazetidines by Asymmetric Allylic Amination of Vinyl Epoxide

Pd-catalyzed asymmetric allylic amination of rac-vinyl epoxide with unsymmetrical 1,2-hydrazines proceeds with excellent regio- and stereocontrol, which after further ring closure provides differentially protected 3-vinyl-1,2-diazetidines in good yields. The chirality at C-3 exerts stereocontrol over the nitrogen centers in the 1,2-diazetidine with all substituents orientating themselves trans to their neighbors. Efficient functionalization without rupture of the strained ring is demonstrated (e.g., by cross-metathesis), establishing the first general route to C-3-substituted 1,2-diazetidines in enantioenriched form.