86630-09-3

Practical total syntheses of acromelic acids A (1) and B (2), which were scarce natural products isolated from toxic mushroom by Shirahama and Matsumoto, were accomplished in 13 (36% total yield) and 17 steps (6.9% total yield), respectively, from 2,6-dichloropyridine (8). Beginning with regioselective transformation of symmetric 8 by either ortho-lithiation or bromination, nitroalkenes 15 and 16 were provided. Stereoselective construction of the vicinal stereocenters at the C-3, 4 positions of 1 and 2 was performed by a Ni-catalyzed asymmetric conjugate addition of α-ketoesters to the nitroalkenes. Construction of the pyrrolidine ring was accomplished in a single operation via a sequence consisting of reduction of the nitro group, intramolecular condensation with the ketone, and reduction of the resulting ketimine.

Practical total syntheses of acromelic acids A (1) and B (2), which have potent neuro-excitatory activity, were accomplished in 13 (36% total yield) and 17 steps (6.9% total yield), respectively, from 2,6-dichloropyridine (8). Regioselective transformation of symmetric 8 provided nitroalkenes 15 and 16. The pyrrolidine ring was efficiently constructed by Ni-catalyzed asymmetric conjugate addition followed by intramolecular reductive amination.

Acromelic acid A 1 and allo-acromelic acid A 12 were synthesised in a biomimetic fashion. An oxidative cleavage-recyclisation strategy was used to construct the requisite C-4 pyridone from an intermediate catechol.

The syntheses of acromelic acid A 1, allo-acromelic acid A 19 and an approach towards acromelic acid B 2 are described. Palladium (0) catalysed cross-coupling reactions were used to generate C-4 catechol precursors and formation of the pyridone rings was investigated using a biomimetic oxidative cleavage - recyclisation strategy.

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Acromelic acid A, a toxic principle of Clitocybe acromelalga, was synthesized from L-α-kainic acid.The synthesis established the previously inferred structure, and determined the absolute configuration as shown by 1.