The Michael condensation of l,l,2,2-tetracyanoethane with 3-methyl-4-benzylideneisoxazolin-5-one having the Z configuration leads to a heterocyclic spiran with retention of the cis orientation of the phenyl and keto groups. The deviations of the series of bond angles of the spiran from the standard values, the abnormal lengths of the C-C bonds adjacent to the gem-dicyano group, and the appearance of nonbonding >C=O(...)CEN interactions and conjugation effects in the enaminonitrile fragment are discussed.
The Michael condensation of l,l,2,2-tetracyanoethane (TCET) with a,B-unsaturated ketones and aldehyde [2-4] leads to various products: 3-amino-4,7,7-tricyano-2-oxabicyclo[2.2.1] heptanes; 2,6-diamino-l,5-dicyanobicyclo[3.3.0]oct-2,6-dienes; 1,8-dialkyl(aryl)-4,4,5,5tetracyanooctane-l,8-diones; 2-amino-l,5,5-tricyano-l-cyclopentenes. The reactions are regioselective; each enone corresponds to one specific product. The direction of the reactions is controlled [5] either by the conformational stereoelectronic situation in the intermediate enolate anion (I) or by the thermostability of the intermediate (II), containing a cyclic n-conjugated system. In the present work we describe the synthesis and the stereochemical and structural characteristics of the spiran (III), produced in the reaction of TCET with 3-methyl-4-benzylideneisoxazolin-5-one.
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