The addition of N-methy ltriazolinedione (M) to biadamantylidene (A gi
ves the [2 + 2) adduct P, but clearly does not proceed in one step bec
ause an aminoaziridinium intermediate if) can be observed to build up
during the reaction. The overall rate of P formation correlates with t
he amount of I that builds up, but not with any sol,ent polarity param
eter despite the fact that charge-separated intermediates are involved
. NMR experiments established that the equilibrium constant for I form
ation is >1000 M-1 in CDCl3 greater than or equal to 500 M-1 in CD2Cl2
and in the range ca 2-15 M-1 for C6D6 and CP6Br5. It is very unlikely
that I is directly on the reaction pathway between M+A and P, and it
is proposed that the zwitterionic intermediate with one CN bond, X, Is
the probable precursor of both I and P, although X does not build up
in concentration enough to be observed CH hydrogen bonding stabilizing
both X and I in chloroform is suggested as a possible rationalization
for the correlation beta een overall rate of P formation and stabilit
y of I relative to the starting materials. Formation of P in benzene i
s catalyzed by Meldrum's acid. M unfortunately reacts too rapidly with
compounds containing OH bonds to study formation of P in the presence
of strong hydrogen bonding reagents. (C) 1997 by John Wiley & Sons, L
td.