Total Synthesis and Stereochemistry of Alternaric Acid

Abstract

Determination of the stereochemistry and the total synthesis of altemaric acid 1 has been achieved. The stereostructure of 1 has been elucidated by stereoselective synthesis of four diastereoisomers of the C(9)-C(14) fragment 6, which had been obtained as a degradation product during structural studies. Key reactions of the total synthesis of 1 include the Julia olefination of tertiary aldehyde 6 and phenylsulfone 7 and novel one-pot construction of 3-acyl-4-hydroxy-5,6-dihydro-2-pyrone via Fries-type rearrangement of the O-enol acyl group of /3-keto-ó-valerolactone toward the a-position of the ó-lactone. The absolute configuration of altemaric acid has been shown to be that illustrated in structure 1. The modified Fries-type rearrangement method has also been extended to the synthesis of some other compounds containing a tricarbonylmethane structure.

Synthesis and organoleptic properties of various 3-methyl-2-oxopentanoates, 2-hydroxy-3-methylpentanoates, and 2-acyloxy-3-methylpentanoates

“…In this series, the unusually strong walnut character of 3 5 was immediately recognized to be of interest to perfumery 6 and it was thus decided to prepare and evaluate the two enantiomers, (+)-3 and (−)-3. , respectively. Thus, using a known method, 7,8 (+)-9 and (+)-10 were converted to α-hydroxy acids (+)-11 and (+)-12, with retention of configuration, in 82 and 93% yields, respectively. Acid-catalysed esterification to ethyl α-hydroxy esters (+)-13 and (+)-14 was then followed by oxidation to (+)-3 and (−)-3, respectively, using pyridinium chlorochromate (PCC; ca.…”

Total Synthesis of (R)- and (S)-semi-Vioxanthin

“…The hydroxy ketone (R)-6 was lactonized to (R)-5,6-dihydro-4-hydroxy-6-methyl-2H-pyran-2-one [(R)-7] by hydrolysis with trifluoroacetic acid. [16] The synthesis was completed by O-methylation with dimethyl sulfate, af- For the preparation of the (S)-enantiomer, a Claisen condensation of tert-butyl acetate and commercially available ethyl (S)-3-hydroxy-butanoate (8) (97% ee) Ϫ which is itself produced by bakers' yeast reduction of ethyl acetoacetate Ϫ was performed, giving tert-butyl (S)-5-hydroxy-3-oxohexanoate [(S)-6]. [17] This compound was converted into pyranone (S)-4 analogously to its enantiomer (Scheme 2).…”

Synthesis of DEFG ring system of cneorins

“…The TBDPS protected anti-cyclopropanolactone 28a was deprotected with tetrabutylammonium fluoride 24 to yield alcohol 29a in modest yield (Scheme 4), which was then transformed into sulfide 30a under the Hata conditions 25,26 and the sulfide was oxidized with m-CPBA to sulfone 31a in excellent yield. Exposure of sulfone 31a to n-BuLi in THF at -100 °C gave the [4.3.1]propellane 32a in 55% yield as a 1:0.8 mixture of two diastereomers at the sulfur bearing carbon.…”