Total synthesis of (-)-tirandamycin A

Total Synthesis of Tyrosine‐Derived Tetramic Acid Pigments from a Slime Mould

“…The acylating agent can then be derived from diketene [8] or from the equivalent 2,2,6-trimethyl-1,3-dioxin-4-one ( Figure 3). [7,9] Figure 3.…”

“…The TBS group was preferred to the TBDPS group because the former gave better yields for the deprotection step despite the fact that it was less stable un-der the basic reaction conditions used for the Lacey-Dieckmann condensation. The 2,4-dimethoxybenzyl (DMB) group was chosen for amide protection on the basis of literature precedent [8,9] and was installed on amine 9a in 83 % yield by reductive amination in the presence of 2,4-dimethoxybenzaldehyde. We will see later that this protecting group proved essential to the Lacey-Dieckmann cyclization.…”

“…[11] In this article we wish to report an alternative method based on Schlessinger's seminal work. [8] Our results provide a general one-pot process for the synthesis of functionalized tetramic acids. This was applied to the synthesis of pigments 5 and 6 ( Figure 2) responsible for the bright yellow to orange color of the myxomycetes slime mould Leocarpus fragilis (see the graphical abstract for a picture of the mould).…”

“…This strategy has been applied to the synthesis of naturally occurring tetramic acids, occasionally with some variations to introduce the acyl side chain. In the 1980s, the method was developed by Boeckman [7] and by Schlessinger [8] who focused on the synthesis of unsaturated 3-acyltetramic acids by way of phosphorus-activated intermediates. Recent examples include the synthesis of macrocidin A (4) by Suzuki [9] or (+)-cylindramine A by Phillips.…”

Novel Syntheses of (E)- and (Z)-Volkendousin, Cytotoxic Steroids from the Plant Melia volkensii

“…Unfortunately, the diacetate 7 proved to be basesensitive, giving a complex mixture of compounds formed from concurrent C-3 and/or C-4 deacetylation [8] and from partial decomposition. Even when using milder protocols, [9] the result was invariably partial C-3 and C-4 deacetylation, decomposition, and recovery of unchanged starting material. To minimize the base sensitivity of pregnane 7, we decided to transform the 3β,4β-diacetoxy moiety into a 3,4-acetonide (Scheme 2).…”