Further Studies on the Direct Synthesis of α , β ‐Unsaturated Ketimines and α , β ‐Enones by Chemoselective Dehydrative Addition of Functionalized Alkenes to Secondary Amides

Described in this paper are the results of an investigation on the extension of the C‐H alkyliminylation and acylation of alkenes with secondary amides. The nucleophilic partner has been extended to cover a series of functionalized alkenes bearing functional groups including ester, α , β ‐unsaturated ester, uncongested ketone groups, as well as enol derivatives of acetaldehyde such as enol ether and enamides. The electrophilic partner has been extended from N ‐(2,6‐dimethylphenyl) and N ‐methyl amides to N‐n ‐butyl, and N ‐cyclohexyl amides. The results demonstrated that the method can be used to synthesize a number of functionalized α , β ‐unsaturated ketimines and α , β ‐enones in an efficient, high yielding, and one‐pot manner. The method was applied to a concise synthesis of ( E )‐6‐styryltetrahydro‐2 H ‐pyran‐2‐one ( 5 ), an immediate intermediate in the syntheses of a series of styryllactone natural products including (±)‐goniothalamine ( 6 ), (±)‐goniothalamine oxide ( 7 ), (±)‐goniodiol ( 8 ), (±)‐leiocarpin A ( 9 ), (±)‐9‐deoxygoniopypyrone ( 10 ), and (±)‐7‐ epi ‐goniodiol ( 11 ).