We formulate scission of the carbon-mercury bond by iodine as an SEi process, depicted in (3) [41. Since this should proceed also with other reagents, it should be possible to prepare further hetero-substituted diazoacetic esters from the compound ( I ) 151. Photolysis of (2) (450 W Hanovia lamp, Pyrex filter) gave ethoxycarbonyliodocarbene (4), from which we obtained ethyl l-iodo-2,2-dimethylcyclopropanecarboxylate (5) (b.p. 45 "CiO.4 mm; yield 40%; NMR signals of the cyclopropane protons as an AB spectrum at T = 8.7 with JAB w 6 Hz) on irradiation of (2) in isobutene until evolution of nitrogen ceased. Products formed by insertion in the C-H bond were not detectedr61. We conclude that the carbene (4) is more selective than ethoxycarbonylcarbene.

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