Construction of the Myrioneuron alkaloids: a total synthesis of (±)-myrioneurinol.

A strategy has been developed that culminated in a stereoselective total synthesis of the tetracyclic antimalarial Myrioneuron alkaloid myrioneurinol. The synthesis relies on three highly diastereoselective reactions, including an intramolecular chelation-controlled Michael spirocyclization of an N-Cbz-lactam titanium enolate to an α,β-unsaturated ester for construction of the A/D-ring system and the attendant C5 (quaternary), C6 relative stereochemistry; a malonate enolate conjugate addition to a nitrosoalkene in order to install the appropriate functionality and establish the configuration at C7; and an intramolecular aza-Sakurai reaction to form the B-ring and the accompanying C9 and C10 stereocenters.

Total synthesis of the tetracyclic antimalarial alkaloid (±)-myrioneurinol.

The first total synthesis of the tetracyclic antimalarial Myrioneuron alkaloid (±)-myrioneurinol has been accomplished using three highly diastereoselective reactions as pivotal steps: 1) an intramolecular Michael addition of a benzyloxycarbonyl-protected lactam titanium enolate to an α,β-unsaturated ester for construction of the spirocyclic C5 quaternary center and the a/d rings, 2) a malonate anion conjugate addition to a transient nitrosoalkene to install the requisite functionality and configuration at the C7 position, and 3) an intramolecular sulfonyliminium aza-Sakurai reaction to form the b ring and the attendant C9/C10 configuration of the natural product.

Experimental evidence of a cyclopropylcarbinyl conjugative electronic effect.

Bicyclo[3.2.0]hept-2-enes undergo thermal rearrangement to norbornenes via diradical transition structures.