The Reaction of Fe CO 3 dab with Dimethyl Acetylenedicarboxylate

stable analogues of 2 could be obtained. The crystal and molecular structures of homologues of 2 could be determined in the iron system, for ruthenium and manganese.  

With the formation of 2, two interdependent stereocentres are formed, the bridgehead iron and carbon atoms. The imine carbon atoms in 1 are prochiral, and the alkyne can approach either of them from either the re- or the si-face. With chiral substituents at the nitrogen atoms, the approach of one face may be favoured over the other. This would lead to diastereoselectivity which has been investigated with different types of diazadiene ligands and a series of chiral N-substituents. Depending on both the type of diazadiene (C2 and non-C2 symmetric) and the chiral N-substituents, diastereoselectivities from 0 to 99% have been observed. 

2 The Isolobal Relation of the Fe-N=C Fragment with an Azomethine Ylide 

Huisgen defined a 1,3-dipoleas a species that may be described (as in Equation 1) by zwitterionic octet structures 6a - 6b, and which may undergo cycloaddition reactions of the type 3 + 2 - 5 with suitable multiple bonds (dipolarophile d=e) to give a neutral five-membered ring 7. 

This general description of a 1,3-dipole can be easily recognised in the iron-imine system with the aid of the isolobal relation 8 and 9 (Equation 2) and, derived from it, 10 and 11 (Equation 3). 

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