Efficient synthesis of new imidazo[1,2-b][1,2]benzothiazine 4,4-dioxide derivatives via lateral lithiation of N-mesitylenesulfonyl hydantoins

N-Mesitylenesulfonyl hydantoins, readily available from commercial α-amino acids, undergo lateral lithiation with an excess of lithium diisopropylamide and tetramethylethylenediamine in the presence of trimethylsilyl chloride to provide new imidazo[1,2-b][1,2]benzothiazin-2-one 4,4-dioxide derivatives in yields ranging from 44–65%.