CYCLOADDITION PRODUCTS FROM (1-DIAZO-2-OXOALKYL)SILANES AND CYCLOPROPENES - A SILATROPIC 2,3-DIAZABICYCLO[3.1.0]HEX-3-ENE/1,4-DIHYDROPYRIDAZINE EQUILIBRIUM

(1-Diazo-2-oxoalkyl)silanes la-h react with cyclopropene 4 to form 2-silyl-2,3-diazabicyclo[3.1.0]hex-3-enes 5 and/or I-silyl-1,4-dihydropyridazines 6. In most cases, a temperature- and solvent-dependent equilibrium 5 reversible 6 maintained by an N --> N' silyl shift exists in solution. With cyclopropene 10, only the 1-silyl-1,4-dihydropyridazines 11 are obtained. None of the 1:1 adducts corresponds to the product expected from a [3 + 2] cycloaddition reaction between the components. Evidence is presented that 1-diazo-2-siloxy-1-alkenes 2 are initially formed from 1 by a 1,3-(C --> 0) silyl shift and are then trapped by the cyclopropene in a 1,3-dipolar cycloaddition reaction.