Highly chemoselective oxidation of 1,5-diols to δ-lactones with TEMPO/BAIB

Total synthesis of the marine cyanobacterial cyclodepsipeptide apratoxin A

“…Reductive opening of lactone 12 with lithium aluminum hydride provided diol 13, which was bis-silylated with TESCl to yield 14. Selective silyl ether cleavage and oxidation of the resultant alcohol 15 delivered aldehyde 16 (27). Alternatively, 16 could be obtained directly from 14 under Swern oxidation conditions (28).…”

Chemical Synthesis of the GHIJK Ring System and Further Experimental Support for the Originally Assigned Structure of Maitotoxin

“…Subsequent reduction of 29 under Luche conditions (NaBH 4 , CeCl 3 ·7 H 2 O) led stereoselectively to the corresponding hydroxy compound (a isomer) whose hydroboration/oxidation (BH 3 ·THF; NaOH, H 2 O 2 ) proceeded regioand stereoselectively to afford, after protection of the resulting diol with TESOTf in the presence of 2,6-lutidine, the bis-TES silyl ether 30 in 65 % overall yield for the three steps. Lactone 31 was then derived from bis-pivaloate 30 by reduction with DIBAL-H, followed by oxidation of the resulting diol mediated by a PhI(OAc) 2 /TEMPO catalyst [16] (82 % overall yield). Lactone 31 was finally converted into the requisite coupling partner, vinyl triflate 33, in 93 % yield by treatment with KHMDS and Comins reagent (32) in THF at À78 8C, thus setting the stage for the casting of the final two rings.…”

Total Synthesis of Marine Natural Products: Cephalosporolides

“…The triple bond was reduced by hydrogenation and removal of the tetrahydropyran protecting group provided the diol 29. Selective oxidation of the primary alcohol using BIAB-TEMPO [24] to the aldehyde, which without chromatographic purification, was converted into the corresponding acid 30 by Pinnick oxidation. [25] Yamaguchi macrolactonization in refluxing toluene provided the eight-membered lactone 31.…”