α‐Oxygenated Crotyltitanium and Dyotropic Rearrangement in the Total Synthesis of Discodermolide

Relative Stereochemical Determination and Synthesis of the C1−C17 Fragment of a New Natural Polyketide

“…Concerning the trienic portion, an inconsistency was immediately noticed. Indeed, a large difference in 13 Ca n d 1 HN M R chemical shifts was observed between compound A and all diastereomers with a decreasing impact from position 1 to 7 (Figure 4).…”

“…To prove this assumption and to determine whether this could affect the polypropionate section or not, a model compound 21 was synthesized 25 and converted into its corresponding sodium carboxylate salt 22 (Scheme 10). A chemical shift deviation profile was observed for carbons C1-C7 by 13 C NMR data comparison between compounds 21 and 22. Because this deviation was similar to that observed between diastereomers 1a-f and A, natural compound A was then deduced to be extracted as a carboxylate salt, but the nature of the counterion could not be determined.…”

“…The differences in the 13 C NMR spectra are highlighted in Figures 6 and 7 by plotting the chemical shift difference observed for each carbon of the C8-C13 portion between natural product A and 1a-f.…”

Asymmetric synthesis of (+)-passifloricin A and its 6-epimer

“…Treatment of lactone 15a with 4 N HCl in THF resulted in cleavage of the MOM-ether and benzylidene acetal to afford passifloricin A (1a) in 89% yield. 19 The other diastereomer 2b was also subjected to the same sequence of reactions to realize the 6-epimer 1b. The spectroscopic data of both compounds 1a and 1b were in full agreement with those reported in the literature.…”

Nitroxide‐Catalyzed Alcohol Oxidations in Organic Synthesis

“…Reactions on a large scale have been described, 60,136 and continuous-process oxidation schemes have been devised. 137 The power of this method can be gleaned from a number of typical examples that illustrate its speed, selectivity and functional group compatibility of the reactions (Schemes 12.30 138 and 12.31 139 ). Notably, no racemization of chiral centers was observed, even when located adjacent to carbonyl groups (Scheme 12.30).…”