A Diversity-Oriented Approach to Spirocyclic and Fused Hydantoins via Olefin Metathesis

An efficient and general method is reported to prepare
a diverse
series of 5,5-spirocyclic and 1,5-, 4,5-, and 3,4-fused bicyclic imidazolidinone
derivatives based on selective alkylation and ring closing metathesis
(RCM) by exploiting the four possible points of diversity in the hydantoin
ring. Hydantoins containing trienes and tetraenes undergo selective
RCM and cross metathesis to afford functionalized spirohydantoins.
A tandem metathesis sequence involving ring closing–ring opening–ring
closing and cross metathesis (RC–RO–RC–CM) occurred
with a hydantoin triene to give a bicyclic hydantoin dimer in high
yield. The fused bicylic dimer could participate in cross metathesis
to produce a functionalized fused hydantoin derivative. The methodology
establishes novel routes to unnatural amino acids, proline homologues,
and cyclic vicinal diamines.