A 12-step synthesis of the ABC carbocyclic core of norzoanthamine is described. It features an organocatalytic asymmetric intramolecular aldolization to set the stereochemistry of the entire molecule, a fragment coupling by selective alkylation of a bis-enolate, and a transannular Michael reaction cascade for rapid and stereoselective synthesis of the polycyclic core.

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We systematically explored a transannular Michael reaction cascade for stereoselective synthesis of polycyclic systems. Both E,Z- and E,E-1,7-bis-enones in the form of 14-membered macrocyclic lactones underwent transannular cyclization to give polycyclic products with high efficiency and excellent diastereoselectivity. In contrast, Z,E- and Z,Z-macrocyclic lactones did not cyclize under similar reaction conditions. Our study revealed similarities and subtle stereochemical differences between this transannular cyclization process and transannular Diels-Alder reactions. An acyl ketene approach was developed for efficient synthesis of macrocyclic lactones. This investigation also illuminated the scope and limitation of macrocyclization by intramolecular Reformatsky reaction to prepare macrocyclic lactones.

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5 R , 7 S ) -K u r z i l a c t o n e a n d i t s ( 5 S , 7 R ) -e n a n t i o m e r Abstract: Natural kurzilactone (5R,7S) and its (5S,7R)-enantiomer were synthesized by a convergent approach using a diastereoselective Mukaiyama aldol reaction to construct the anti diol unit. Finally, a ring-closing metathesis reaction led to the target molecule.

Bismuth(III) chloride was found to be an efficient catalyst for the transesterification of a variety of β‐keto esters with a wide range of alcohols to afford transesterified products in good to high yields in short reaction times (see Table).