Transmetalation of cyclic aminostannanes

From the failure to transmetalate branched acyclic aminostannanes, one might conclude that secondary a-aminoorganolithiums are either thermodynamically unstable or kinetically inaccessible. However, following the maxim 'There's no excuse for not doing the experiment', the Gawley group found that secondary cyclic a-aminoorganolithiums 13 are formed readily at low temperature by tin-lithium exchange on the stannanes 12 (eqn. 9). [1,2]
Now, the question arises: Why is it possible to easily transmetalate primary and cyclic secondary a-aminoorganostannanes, but not secondary acyclic ones? The short answer is that we don't know, but this poster describes some of the possibilities we have considered. Unfortunately, testing these hypotheses has not led to a definitive answer, so we submit our thoughts and preliminary data to the organic community for advice and suggestions. Click here to see two hypotheses.

Note: The difference cannot be due to the simple fact that the nitrogen is part of a ring. Click here to see an example where a tin compound with a pyrrolidine-type nitrogen does not transmetalate.


1. Gawley, R. E.; Zhang, Q. J. Am. Chem. Soc. 1993, 115, 7515.
2. Gawley, R. E.; Zhang, Q.; Campagna, S. J. Am. Chem. Soc. 1995, 117, 11817.

Back to the introductory page
1. Transmetalation of acyclic aminostannanes: Primary organolithiums can be formed, but secondary organolithiums cannot
2. Transmetalation of cyclic aminostannanes: Secondary organolithiums are formed. (THIS PAGE)
3. Hypotheses: Conformational effects (i.e., a kinetic problem) or thermodynamics may be responsible
4. These studies allow a ranking of the relative stabilities of organolithiums
5. How the aminostannanes were made.