A total synthesis of lasalocid A

Abstract

Communications to the Editor 2933 the N2C5CI4 molecule is not known. The Ir-N(l) (1.819,1.794 Á) and N(l)-N(2) (1.171,1.159 Á) distances, while similar, are consistent with less it back-bonding from metal to atom N(l) in the N2R species.We believe that the route to a variety of metal-NaR complexes described here is general one and that the comparative reaction and structural chemistry of these complexes and their CO, NO+, and N2Ph+ analogues will prove to be diverse and interesting.

(Schiff‐base)vanadium(V) Complex‐Catalyzed Oxidations of Substituted Bis(homoallylic) Alcohols − Stereoselective Synthesis of Functionalized Tetrahydrofurans

“…[8,15] From a historical point of view, the reagent combination of [VO(acac) 2 ] [acac ϭ acetylacetonato(Ϫ1)] and TBHP was the first and in the following years most frequently applied oxidant for converting bis(homoallylic) alcohols, by a transition metal catalyzed oxidation, into functionalized tetrahydrofurans. [2,16] This procedure has been successfully applied for the synthesis of tetrahydrofuran subunits of polyether-derived natural products such as lasalocid A, [17] ionomycin, [18] teurilene, [19] ferensimycin B, [20] glabrescol, [21] venustatriol, [22] or thyrsiferol. [23] Surprisingly, until now this method has not been further explored, either (i) by conducting a concise structure-selectivity survey or (ii) by application of auxiliaries other than exclusively diketonate ligands, in order to improve the reactivity and stereoselectivity of the active oxidant.…”

Synthetic Study of Marine Polycyclic Ethers: Total Synthesis of Hemibrevetoxin B.

“…This type of rearrangement was first reported during the total synthesis of lasalocid A (ref. 11), in which the rearrangement of the tetrahydrofuran to a tetrahydropyran system was accomplished by treatment with Ag2CO3 in acetone-H2O. The rearrangement of 8a was first investigated under the original reaction conditions, i.e., upon treatment with Ag2CO3 in acetone-H2O at reflux for 24 h, the rearrangement took place giving the ring-expanded ether 11 in 46% yield along with the recovered starting material 8a (39%).…”

Epoxides in Complex Molecule Synthesis

“…Epoxidation of bishomoallylic alcohol 3 by TBHP/VO(acac) 2 by this approach, followed by treatment of the intermediate epoxide 4 with acetic acid, gave the THF derivative 5 of isolasalocid A (a 5-exo cyclization; Scheme 8.2) [11]. Further epoxidation of 5 (a g-alkenol) under the same conditions, followed by acetylation, afforded epoxide 6.…”