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COMMUNICL4TIONS T O THE EDITOR I,4-ADDITJON OF OZONE TO FURANS AND PYRROLES
felt that the "abnormal" reactions are the result of the l,il--addition of ozone. We wish now to reSir: port confirmatory evidence for this. When the ozonolysis just described was stopped Wibaut and co-workers1.2 have obtained products from the ozonolyses of methylated pyrroles after the absorption of one mole equivalent of ozone and furans which cannot be accounted for by cleav- and the reaction mixture was partially evaporated, age of the double bonds in the normal structures of a 12% yield of cis-l,2-dibenzoylethylene(VII) these substances. Similarly, we have obtained a precipitated (m.p. 130-135°, identification by a 147, yield of phenylglyoxal (VIII) from ozonolysis mixture melting point with an authentic sample4) of 2,5-diphenylfuran (I). The solvent was a Similar results were obtained using a mixture of methanol-acetone mixture, the temperature was ozone and nitrogen instead of ozone and oxygen, -40°, two mole equivalents of ozone were ab- showing definitely that the reaction is one of ozone sorbed, the peroxidic ozonolysis products were re- and not of oxygen. This material cannot arise from ozonolysis of duced with hydrogen over palladium catalyst and the other major product was benzoic acid (81y0 11. The furan ring has been cleaved but the 3,4 bond is still intact. The cis configuration, which yield). T.S'ibaut and co-workers1j2 have explained "ab- is that of the labile isomer,6 proves that the double normal" results such as these as being reactions of bond a t the 3 and 4 positions was formed before the ionic structures such as 11. It hardly seems likely, ring was cleaved. This can occur only by a 1,4however, that ozone would polarize the molecule addition of ozone to the conjugated system of the to, and attack, such an unstable structure as 11, furan. Any one of structures III, IV or V could especially since the reactive positions of the furan have been the intermediate. We believe a similar mechanism holds true for m d pyrrole ring systems are 2 and 5.3 We have the reactions of Wibaut and ~o-rnorkers.'~~ FurH -C
