A highly efficient, one-pot synthesis of ring-fused 5-hydrazino-2-cyclopentenone
derivatives is achieved by a gold(I)-catalyzed cycloisomerization/hetero-Diels–Alder/ring-opening
tandem reaction of suitable enynyl acetates. By mixing the latter
with a dialkylazodicarboxylate in the presence of a gold(I) catalyst,
the 1,3-acyloxy migration/Nazarov cyclization process leads to dienyl
acetate intermediates which are trapped by the heterodienophile present
in situ. This provides strained intermediates which undergo highly
regioselective ring opening by a retro aza-Michael reaction promoted
by traces of water, eventually yielding the target compounds. Six-
and seven-membered ring-fused cyclopentenones and piperidine- and
tetrahydropyran-fused cyclopentenones bearing a pendant hydrazino
functionality on a bridgehead carbon atom can be obtained in high
yield (68–96%) by this approach.