Synthesis of 6’ H-spiro(indene-2,2’ -[1,3]oxathiane)-1,3,5’ -triones

Reaction of ninhydrin with α -mercapto carboxylic acids or the corresponding Bunte salts affords 6 ’ H -spiro(indene-2,2 ’ -[1,3]oxa- thiane)-1,3,5 ’ -triones.