Annuloselectivity And Stereochemistry In The Reaction Of Ketenes And Sulfonyl Chlorides With Imines

There exist four annulations between ketenes and imines, namely [2~k+2~i], [2~k+2~i+2~k], [2~k+2~k+2~i], and [2~k+2~i+2~i] annulations. Between sulfonyl chlorides and imines, two annulations exist:[2~s+2~i] and [2~s+2~i+2~i] annulations. In the studies on the selectivities between the above annulations (annuloselectivities), the following results were achieved.(1) Base-switched [2~k+2~i] and [2~k+2~k+2~i] annuloselectivity between ethoxylcarbonyl ketenes and linear imines:in the presence of 2-chloropyridine, only [2~k+2~i] annulation occurs, while in the presence of N-methylimidazole, [2~k+2~k+2~i] annulation occurs exclusively. The stereochemistry of the three stereocenters in the [2~k+2~i+2~i] annuladducts is experimentally disclosed, and a model based on hetero-Diels-Alder cycloaddition is proposed to explain and predict the stereochemical outcomes.(2) Starting from alkyl halides and thiourea, three environment-and worker-friendly, convenient, and practical methods to prepare sulfonyl chlorides are developed, that is,N-chlorosuccinimide method, sodium chlorite method, and sodium hypochlorite method.(3)The stepwise mechanism in the [2s+2i] annulations (sulfa-Staudinger cycloaddition) are proposed as following: the conrotatory ring closure of the key 2,3-thiaza-butadiene-type zwitterionic intermediates. The models to explain and predict the diastereoselectivity of the [2s+2i] annulations are proposed. The substituent-dependent [2s+2i] and [2s+2i+2i] annuloselectivities are discovered, and a guideline is put forward to predict the annuloselectivity and stereochemistry of the two annuladducts.(4)The diazosulfonamides are first reported, and find utility in the syntheses of benzo-y-sultams via the Rh-catalyzed intramolecular aromatic C-H functionalization.