In this report, several new epoxide examples were united with β-silyl ketone enolates for the construction, after oxidative fragmentation, of ring expanded lactones, n+3 atoms in size. Importantly, azido lactones were found to be valuable in an extension of this protocol involving the n+3+p expansion into a series of hydroxyolefinic lactams. We also document a short, stereoselective total synthesis of (+)-cis-lauthisan and a new, cuprate-mediated and HMPA-free procedure for the generation of β-silyl silylenol ethers, useful in the environmentally-friendly construction of medium sized lactones.

For the past 50 years, Professor Gary H. Posner has made a significant impact on the field of synthetic organic chemistry. This short review aims to briefly highlight just some of his major contributions, including: (1) early work in the development of organocopper chemistry, specifically cross coupling reactions and the synthesis of non-symmetrical ketones; (2) chiral transfer reactions using both chiral sulfoxides and selenides for the construction of complex products; (3) [4+2]-reactions exploiting 3-substituted pyrones; and (4) novel domino reaction cascades for the synthesis of carbocycles and ring expanded lactones.

The first asymmetric total synthesis and revision of the relative configuration of the 12-membered taumycin A macrocycle is described. Key to the success of this work was a novel α-keto ketene macrocyclization that provided an efficient means by which to access two diastereomers of the desired macrolide without the need to employ additional coupling agents or unnecessary oxidation state adjustments.

A small library of synthetic (−)-palmyrolide A diastereomers, analogues, and acyclic precursors have been examined with respect to their interaction with voltage-gated sodium channels (VGSCs). Toward this goal, the ability of (−)-palmyrolide A and analogues to antagonize veratridine-stimulated Na+ influx in primary cultures of mouse cerebrocortical neurons was assessed. We found that synthetic (−)-palmyrolide A and its enantiomer functioned as VGSC antagonists to block veratridine-induced sodium influx. A detailed NMR and computational analysis of four diastereomers revealed that none had the same combination of shape and electrostatic potential as exhibited by natural (−)-palmyrolide A. These data indicate that the relative configuration about the tert-butyl and methyl substituents appears to be a prerequisite for biological function. Additional testing revealed that the enamide double bond was not necessary for blocking veratridine-induced sodium influx, whereas the acyclic analogues and other macrolide diastereomers tested were inactive as inhibitors of VGSCs, suggesting that the intact macrolide was required.

The first asymmetric total synthesis and determination of the absolute configuration for the neuroactive marine macrolide palmyrolide A is described. The highlight of the synthesis is macrocyclization via trans-enamide formation catalyzed by copper(I) iodide and cesium carbonate. Comparison with the authentic spectral data confirms the synthesis of (+)-ent-palmyrolide A.

A full account of our synthetic work toward the first total synthesis of the neuroactive marine macrolide (−)-palmyrolide A is described. Our first-generation approach aimed to unlock the unknown C(5)–C(7) stereochemical relationship via the synthesis of four diastereomers of palmyrolide A aldehyde, a known degradation product. When these efforts provided inconclusive results, recourse to synthesizing all possible stereocombinations of the 15-membered macrolide was undertaken. These studies were critical in confirming the absolute stereochemistry, yielding the first total synthesis of (+)-ent-palmyrolide A. Subsequent to this work, the first protecting-group-free total synthesis of natural (−)-palmyrolide A is also reported.