One‐Pot Gold(I)‐Catalyzed Rautenstrauch Rearrangement/Nitrosocarbonyl Hetero‐Diels–Alder Reaction Sequence for the Synthesis of α‐Hydroxylated Cyclopentenones

The synthesis of densely functionalized, ring-fused α-hydroxy-2-cyclopentenone precursors is achieved by one-pot gold(I)-catalyzed Rautenstrauch/hetero Diels−Alder/ring opening sequential reactions of suitable propargyl esters. The 1,2-acyloxy migration/cyclization process (Rautenstrauch reaction) leads to cyclopentadienyl ester intermediates which are stereo- and regioselectively trapped by the nitrosocarbonyl reagent generated in situ by adding a hydroxamic acid (e.g., Boc-NHOH) and an oxidant (n-Bu4NIO4) to the reaction mixture after the Au(I)-catalyzed cycloisomerization step. This provides strained intermediates, which undergo highly regioselective ring opening by a retro-aza-Michael reaction triggered by hydrolysis of the acetate group, eventually yielding the precursors of racemic, ring-fused α-hydroxy-2-cyclopentenone compounds in 46%–90% yield. The target six-, seven-, and eight-membered ring-fused cyclopentenones bearing a tertiary α-hydroxy group can be then obtained in moderate to good yield (42%–84%) by N-O cleavage in the presence of Mo(CO)6.