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

Direct Access to CF3-Containing 4H-1,3-Oxazines and 2-Aminopyrimidines Via a [4 + 2] Annulation Using In Situ Generated Carbodiimide Anions

The carbodiimide anions which were generated in situ from N-cyano-N-aryl-p-toluenesulfonamides (NCTS) in the presence of the base participated in annulations that remain less reported to date. Herein, we have developed for the first time an efficient and environmentally friendly [4 + 2] annulation reaction of CF3-substituted hetero-1,3-dienes with NCTS for the efficient synthesis of CF3-substituted 4H-1,3-oxazines and 2-aminopyrimidines under transition-metal-free conditions. The methodology demonstrates the advantages of readily available substrates, simple operation, good functional group tolerance, and broad substrate scope, providing a promising route to the synthesis of structurally diverse CF3-substituted scaffolds. The products followed by simple transformations provide a facile route to TAS2R14 agonist analogues.

Direct Synthesis for Benzofuro[3,2-d]pyrimidin-2-Amines via One-Pot Cascade [4+2] Annulation/Aromatization between Benzofuran-Derived Azadienes and Carbodiimide Anions

The chemoselective [4+2] annulation/aromatization reactions between benzofuran-derived azadienes and N-Ts cyanamides are developed, affording a convenient method for synthesizing benzofuro[3,2-d]pyrimidin-2-amines under mild conditions. Herein, N-Ts cyanamides participated in reactions selectively via carbodiimide anion intermediates and the corresponding cyanamide anion intermediates derived products were not observed. The proposed chemoselective stepwise reaction mechanism was well supported by DFT calculations.

(Dimethylamino)methylene hydantoins as building blocks in the synthesis of oxoaplysinopsins and parabanic acids with antifungal activity

A short, efficient, and stereoselective methodology is described for the synthesis of 5-((dimethylamino)methylene)hydantoins and their conversion into oxoaplysinopsins and parabanic acids. A highly convergent one-pot, two-step reaction between methyl N-arylglycinates, isocyanates, and DMFDMA under microwave irradiation provided the corresponding (dimethylamino)methylene hydantoins as a single E-stereoisomer in high overall yields. The synthesis of (S)-1-(1-phenylethyl) chiral hydantoins, which undergo a stereoselective addition of acetic anhydride, aza-heterocycles, and amines, received special attention. The reaction with indole delivered a series of novel oxoaplysinopsins. Meanwhile, parabanic acids were prepared by a new approach, treating (dimethylamino)methylene hydantoins with mCPBA to generate the oxidative fragmentation of the exocyclic methylene. The antifungal evaluation of the prepared products was carried out on a series of Candida spp., finding potent growth inhibition. According to previous docking studies, this activity is probably due to the inhibitory interaction of the derivatives with the active site of the fungal HMGR enzyme.

Visible Light-Enhanced [3 + 2] Cycloaddition of N,N-Disubstituted Hydrazines with Organo-Cyanamides: Access to Polysubstituted 1,2,4-Triazol-3-amines

Visible light-enhanced [3 + 2] cycloaddition of N,N-disubstituted hydrazines with N-cyano-N-aryl-p-toluenesulfonamides is an efficient reaction pathway to polysubstituted 1,2,4-triazol-3-amines. The reaction is performed under mild conditions without the addition of any transition metals. This strategy involves a C(sp3)-H bond activation, a cyano cycloaddition, and the formation of two new C═N bonds. The protocol shows the advantages of good functional group tolerance and broad substrate scope. The late-stage modification experiments provide practical applications in the field of organic synthesis and medicinal chemistry.

Silver acetate-catalyzed synthesis of cyclic sulfonyl guanidine with exocyclic double bond

An efficient protocol for the synthesis of cyclic guanidine with exocyclic double bond has been developed. The synthesis has been achieved via intramolecular hydroamination of an intermediate propargyl guanidine by using silver acetate as catalyst in the presence of acetic acid. The reaction proceeds via the formation of acyclic propargyl guanidine in a one-pot reaction of N,N-dibromoarylsulfonamides, isonitriles, and propargylamine in the presence of K2CO3. In the second stage of the synthesis, the acyclic guanidine selectively undergoes 5-exo-dig cyclization in the presence of silver acetate and acetic acid to produce the five-membered cyclic guanidine framework having an exocyclic double bond as the constituent part. Short reaction time, wide substrate scope with good to high yields, and good functional group tolerance are the remarkable achievement of the present protocol.

Organo-cyanamides: convenient reagents for catalytic amidation of carboxylic acids

An unprecedented DMAP-catalysed amidation of aryl and alkyl carboxylic acids with organo-cyanamides has been developed. Unlike the use of N-cyano-N-phenyl-p-methylbenzenesulfonamide (NCTS) as an electrophilic cyanating reagent, an unusual desulfonylation/decyanation reaction model has been disclosed for the first time. Remarkable features of this reaction include readily available substrates, simple operation and broad scope, enabling the efficient synthesis of structurally diverse amides. The synthetic utility of this protocol was demonstrated by the late-stage amidation of bioactive carboxylic acids and a scale-up reaction.

Regioselective and stereospecific synthesis of functionalized 3,4-dihydro-2H-1,4-thiazines by catalyst-free [3 + 3] annulation of pyridinium 1,4-zwitterionic thiolates and aziridines

An efficient route to 3,4-dihydro-2H-1,4-thiazines was developed though [3 + 3] annulation of pyridinium 1,4-zwitterionic thiolates and aziridines under catalyst-free conditions.

Direct synthesis for N2-unprotected five-membered cyclic guanidines by regioselective [3+2] annulation of aziridines and cyanamides

A novel and efficient [3+2] annulation of 2-substituted aziridines and N-tosyl cyanamides via domino regioselective ring-opening/5-exo-dig cyclization procedure has been developed, allowing the direct preparation for N2-unprotected five-membered cyclic guanidines...