Synthesis of 3-Amino-1,2,4-benzothiadi- azine 1,1-Dioxides via a Tandem Aza-Wittig/Heterocumulene Annulation

A Route to Triazole-Fused Sultams via Metal-Free Base-Mediated Cyclization of Sulfonamide-Tethered 5-Iodotriazoles

An efficient direct approach to triazole-fused sultams has been developed. The key step of the proposed strategy is base-mediated cyclization of sulfonamide-tethered 5-iodo-1,2,3-triazoles which are readily available via an improved protocol for Cu-catalyzed 1,3-dipolar cycloaddition. The annulation of the sultam fragment to the triazole ring proceeds smoothly under transition-metal-free conditions in the presence of Cs₂CO₃ in dioxane at 100 °C and affords fused heterocycles in high yields up to 99%. The favorability of an S_NAr-like mechanism for the cyclization was supported by DFT calculations. The applicability of the developed procedure to modification of natural compounds was demonstrated by preparation of a deoxycholic acid derivative.

N-Alkylation and Aminohydroxylation of 2-Azidobenzenesulfonamide Gives a Pyrrolobenzothiadiazepine Precursor Whereas Attempted N-Alkylation of 2-Azidobenzamide Gives Benzotriazinones and Quinazolinones

N-Alkylation of 2-azidobenzenesulfonamide with 5-bromopent-1-ene gave an N-pentenyl sulfonamide, which underwent intramolecular aminohydroxylation to give an N-(2-azidoaryl)sulfonyl prolinol, a precursor for the synthesis of a pyrrolobenzothiadiazepine. The attempted N-alkylation of 2-azidobenzamide gave a separable mixture (∼1:1) of a benzotriazinone and a quinazolinone in a 72% combined yield. Other primary alkyl halides (3 examples) gave similar mixtures of benzotriazinones and quinazolinones. Benzylic, allylic, and secondary and tertiary alkyl halides (5 examples) gave only benzotriazinones in moderate yields. The results of mechanistic studies show the likely involvement of nitrene intermediates in the quinazolinone pathway and a second pathway involving a dimethylsulfoxide or dimethylsulfide-mediated conversion of 2-azidobenzamide into benzotriazinones.

Intramolecular azide to alkene cycloadditions for the construction of pyrrolobenzodiazepines and azetidino-benzodiazepines

The coupling of proline- and azetidinone-substituted alkenes to 2-azidobenzoic and 2-azidobenzenesulfonic acid gives precursors that undergo intramolecular azide to alkene 1,3-dipolar cycloadditions to give imine-, triazoline- or aziridine-containing pyrrolo[1,4]benzodiazepines (PBDs), pyrrolo[1,2,5]benzothiadiazepines (PBTDs), and azetidino[1,4]benzodiazepines. The imines and aziridines are formed after loss of nitrogen from a triazoline cycloadduct. The PBDs are a potent class of antitumour antibiotics.

One-Pot Three-Component Synthesis of bis[2-(methylthio)-7-oxothiazolo[4,5-d]pyrimidin-6(7H)-yl]benzenes

Three-component reactions of ethyl 2-methylthio-4-[(triphenylphosphanylidene)amino] thiazole-5-carboxylate with aromatic diisocyanates and secondary amines produced novel bis[2-methylthio-7-oxothiazolo[4,5-d]pyrimidin-6(7H)-yl]benzenes in the presence of EtONa in 67–93% yields. This method provides an effective synthesis of nitrogen-containing heterocycles with the advantages of mild reaction conditions, simple operation and good yields. The structures of the products were confirmed by 1H NMR, IR, MS and elemental analysis.

Facile synthesis of benzothiadiazine 1,1-dioxides, a precursor of RSV inhibitors, by tandem amidation/intramolecular aza-Wittig reaction

Reaction of o-azidobenzenesulfonamides with ethyl carbonochloridate afforded the corresponding amide derivatives, which gave 3-ethoxy-1,2,4-benzothiadiazine 1,1-dioxides through an intramolecular aza-Wittig reaction. The reaction was found to be general through the synthesis of a number of benzothiadiazine 1,1-dioxides. Acid-catalyzed hydrolysis of 3-ethoxy-1,2,4-benzothiadiazine 1,1-dioxides furnished the 2-substituted benzothiadiazine-3-one 1,1-dioxides in good yields and high purity, which is the core moiety of RSV inhibitors.

One-Pot Three-Component Synthesis of 1,4-bis[thiazolo[4,5-d]pyrimidin-7(6H)-one]piperazine derivatives

A simple one-pot efficient method is described for the synthesis of 1,4-bis[thiazolo[4,5-d]pyrimidin-7(6 H)-one] piperazine derivatives by a domino three-component process involving an aza-Wittig reaction/heterocyclisation in the presence of sodium ethoxide as catalyst. Ethyl 4-[(triphenylphosphanylidene)amino]-2,3-dihydro-3-phenyl-2-thioxothiazole-5-carboxylate reacted with aromatic isocyanates to give carbodiimide intermediates. This was followed by the addition of piperazines to give the corresponding guanidine intermediates. The guanidine intermediates were then cyclised in the presence of catalytic amount of sodium ethoxide to give 1,4-bis[thiazolo[4,5-d]pyrimidin-7(6 H)-one]piperazine derivatives in good yields.

Applications of phosphine-functionalised polymers in organic synthesis

This tutorial review deals with recent advances in the use of phosphine-functionalised polymers in organic synthesis. In the first part of the review, some recent applications of polymer-supported palladium catalysts are reviewed, particularly recyclable catalysts for C-C and C-X bond formation with aryl bromide and chloride substrates. In the second half, novel applications of phosphine-functionalised polymers as reagents, scavengers, organocatalysts and linkers in organic chemistry are presented. Emphasis is placed on the synthesis of biologically active molecules.