Efficient synthesis of new chiral 1,2-benzothiazin-3-one 1,1-dioxide derivatives via lateral lithiation of 3-N-mesitylenesulfonyl-1,3-oxazolidin-2-ones

Chiral 3-N-mesitylenesulfonyl-1,3-oxazolidin-2-ones 4a–e derived from (l)- and (d)-amino acids 1a–e undergo lateral lithiation with lithium diisopropylamide and TMEDA in anhydrous THF to provide new optically-active 1,2-benzothiazin-3-one 1,1-dioxide derivatives 5a–e with yields ranging from 63% to 79%.