Cycloaddition reactions of dialkylaminobis(trifluoromethyl)boranes with isocyanates and isothiocyanates. Crystal structures of , , and

Article abstract of DOI:10.1016/0022-328X(91)86307-C

The reactions of (CF3)2BNMe2 (D1) and (CF3)2BNEt2 (D2) with isocyanates and isothiocyanates have been studied.At or near room temperature the C=N bonds of RN=C=O and RN=C=S enter into <2 + 2> cycloadditions with the B-N bond of D1 to yield the four-membered rings ; R = Me (I), ^tBu (II), Ph (III), CF3 (IV), and ; R = Me (V), Et (VI), ^tBu (VII), Ph (VIII), and p-FC6H4 (IX) respectively.I, V, VI, VIII and IX rearrange at ca. 60 deg C to form the isomers (XI) and ; R = Me (XII), Et (XIII), Ph (XIV) and p-FC6H4 (XV), respectively.At room temperature D2 reacts with MeN=C=O to yield (X) directly.X and XI reversibly incorporate MeN=C=O to form the six-membered heterocycles ; R = Me (XVI) and Et (XVII).The structures of II, VII, XIV and XVII have been established by single-crystal X-ray diffraction studies.The bond distances indicate that the ?-bonding is delocalized over OCN (sp²), SCN (sp²) and SCN2 (sp²) fragments in II, VII and XIV, respectively.Furthermore, the ?-character of the exocyclic C-N bonds in XIV and XVII, while considerable, is lower than that of the exocyclic C-O(S) bonds in II, VII and XVII.The other structural assignments were based on mass spectrometry and vibrational and multinuclear NMR spectra.