Beckmann rearrangement, enone

DMF is recommended as diluent in the Ullmann synthesis of diaryls from aryl halides and as solvent for the Beckmann rearrangement of steroidal enone oximes. The Willgerodt-Kindler reaction (a carbonyl compound with a secondary amine and sulfur to give a thioamide) can be carried out in good yield at 50-60 if DMF is... 

A transannular route to 1-substituted pyrrolizidines has recently been reported by Wilson and Sawicki. The lactam (79) was prepared by Beckmann rearrangement of the oxime p-toluenesulfonate of cyclohept-4-enone. Reduction with lithium aluminum hydride gave the amine (80), which on treatment with bromine yielded the 1-bromopyrrolizidine (81) in one stereospecific step (95%). The stereochemistry of the product corresponds to a disfavored exo-mode of cyclization by attack of the nitrogen on the bromonium ion. Further modification of this route to produce naturally occurring alkaloids would appear feasible, but has not yet been reported. 

The optimized Beckmann rearrangement was used to install the amine functionality at the quaternary center of the azaspirodecane core 61 of pinnaic acid and halichlorine (Scheme S.IST Thus, after ketone 54 was converted to the lactam 57, subsequent reductive cleavage and amine protection gave alcohol 59. Elaboration of the PMP-protected hydroxyethyl side chain of 59 provided enone 60, which smoothly underwent a reductive amination to yield the azaspirodecane core 61. This advanced intermediate was then elaborated into the natural products pinnaic acid (52) and halichlorine (53). 

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