Application of the diastereoselective photodeconjugation of α,β-unsaturated esters to the synthesis of gymnastatin H

Abstract

SummaryThe asymmetric synthesis of gymnastatin H has been achieved by using the photoisomerisation of a conjugated ester to its β,γ-unsaturated isomer through the protonation of a in situ generated dienol as key step. Thanks to diacetone D-glucose used as a chiral alkoxy group, the protonation occurred well onto one of the two diastereotopic faces with very high yields and selectivities. Moreover, by this way the configuration of the C-6 centre of the target molecule was controlled.

Cu‐Catalyzed Asymmetric Allylic Alkylation of Phosphonates and Phosphine Oxides with Grignard Reagents

“…The reaction of MeMgBr with phosphonate 1 b proved to be even more efficient, giving the corresponding β‐methyl substituted compound 2 b in 97 % yield (Table 1, entry 3) with near‐perfect S N 2′ selectivity (99:1) and enantioselectivity (99:1 e.r.). This transformation allows for the introduction of a methyl unit, which is the most common and valuable structural alkyl motif for biologically relevant systems 21. The reaction was extended to the related methyl phosphonates (Table 1, entries 4, 5) and phosphine oxides (Table 1, entries 6, 7) by using both methyl and ethyl magnesium bromide.…”

Marine natural products

“…329 Synthesis of unguisin A, a g-aminobutyric acid (GABA)-containing cyclic heptapeptide originally isolated from the fungus Emericella unguis, 330 was completed in good yield via macrocyclisation of a GABA-containing linear precursor 331 and synthesis of the amide gymnastatin H, from the sponge-associated fungus Gymnascella dankaliensis, 332 was accomplished in fourteen steps with a diastereoselective photodeconjugation of a diacetone D-glucose ester as a key step. 333 (+)-Paecilospirone, a metabolite of the tropical fungus Paecilomyces sp., 334 was prepared via an enantioselective method, with an anti-selective lactate-derived aldol reaction and a palladium catalysed double deallylation/spirocyclisation as key steps. 335 It is worth noting that the name paecilospirone was originally given to an unrelated compound from a soil-derived Paecilomyces sp.…”

Asymmetric Allylic Alkylation of Acyclic Allylic Ethers with Organolithium Reagents

“…The presence of a methyl substituent in the allylic ether 2 f, allows for the preparation of a range of synthons with a methyl group at the stereocenter; an important structural moiety that is present in many natural compounds. [18] The compatibility of two ether moieties in the same molecule was demonstrated by the use of allyl substrate 1 g, which bears both an allylic-OMe and -OBn ether, and 2 g, which contains two allylic -OBn moieties ( Table 2, entries 17 and 18). Although the conversion was lower in both cases in comparison with the previous results, the S N 2' selectivity observed was complete, with excellent enantiomeric ratios.…”