With the common intermediate 10 in hand, the stage was
set for the pivotal cross metathesis reaction. Heating a
mixture of 10 and dienoate 8 under reflux (CH2Cl2) for 3 h
in the presence of Grubbs II catalyst (7) (10 mol %) provided
an inseparable mixture of 5 and the dimer of 8.
18,19 Pure 5
(E/Z ) 10:1) could be obtained by a sequence of reactions
involving removal of the N-Boc group, purification of the
intermediate amine, and reinstallation of the N-Boc group
(29% overall yield). Owing to the inefficiency of this process
and practical considerations, we decided to telescope three
reactions. In the event, the azaspirobicycle 15 was prepared