Spiro[1,3-benzoxathiepin-4(5H),1′-cyclohexa[2,4]dien]-2,2′-dione, a Novel Heterocyclic Ring System

Besides the common cyclisation reactions between divalent electrophiles such as Soc1 2 , SC1 2 , etc. and 2,2′-alkylidene-bisphenols 1 with selective attack by the two oxygens yielding dibenzo[d,g][1,3,2]dioxathiocines [1] we observed previously an unusual cyclisation of 1 with S 2 CI 2 with a nucleophilic attack by the ortho- and para-carbon atoms (C(2) and C(4)) of bisphenol 1 [2]. We now report a new type of cyclocondensation reaction of 4,4′,6,6′-tetrasubstituted 2,2′-alkylidene-bisphenols 1 with ClSCOCl affording spiro[1,3-benzoxathiepin-4(5H),1′-cyclohexa[2,4]dien]-2,2′-diones 2 together with the cyclic carbonates 3. The structures of the products were elucidated mainly by l3 C-NMR- and 1 H-NMR-spectroscopy. The mode of formation of the novel spiro thiocarbonates 2 resp. the known carbonates 3 [3] is discussed.