Enantioselective Synthesis of Optically Active O‐Benzoyl‐Protected α‐Hydroxyl‐β,γ‐Unsaturated Acids with Chiral Induction of (S)‐Glyceraldehyde Acetonide

Abstract

α‐Hydroxyl‐β,γ‐unsaturated acids are usually present in biologically active natural products and medicines, and serve as valuable building blocks in synthetic organic chemistry. A new method for the synthesis of O‐benzoyl‐protected α‐hydroxyl‐β,γ‐unsaturated acids is presented. Chiral induction was achieved using (S)‐glyceraldehyde acetonide as chiral source together with ClTi(Oi‐Pr)3 as coordinating agent. The overall synthetic route included 6 simple steps, and six optically active O‐benzoyl‐protected α‐hydroxyl‐β,γ‐unsaturated acids 1 a‐1 f (99% ee) were prepared in up to 53% yield.

Diastereoselective allylation-based asymmetric total synthesis of 1,10-seco-guaianolides

“…Tracing back for the actual natural product, we needed the enantiomer, i.e., ent-3b. The required aldehyde 20 was easily prepared from L-ascorbic acid 19 using a known protocol 10,15 (Scheme 5). This, with an additional two steps, led to the enantiomeric allyl bromolactone ent-3b.…”

“…2, 206.6, 178.0, 164.7, 139.9, 79.3, 47.2, 41.5, 40.3, 33.8, 30.1, 24.9, 24.5, 15.0, 8.9 (S)-2,2-Dimethyl-1,3-dioxolane-4-carbaldehyde (20). 15 AcCl (8.8 mL, 0.124 mol) was added dropwise to a solution of L-ascorbic acid 19 (20 g, 0.110 mol, 1.0 equiv.) in acetone (500 mL) and the mixture was stirred at 40 °C for 2 h. Next, the mixture was cooled to 0 °C and filtered.…”

A Sphingolipid Fatty Acid Constituent Made by Alkyne trans‐Hydrogenation: Total Synthesis of Symbioramide

“…Although (À )-2 as the common fatty acid constituent of these natural products is a deceptively simple compound, a truly practical synthesis has not yet been reported. While most of the early approaches to 1 and (À )-2 resorted to the chiral pool or invoked chiral auxiliaries, [19][20][21][22][23] the known catalysis-based routes are either unduly lengthy, insufficiently selective, or mandate the use of stoichiometric amounts of organoselenium reagents as reaction partners, which render upscaling inconvenient. [24][25][26] The arguably most advanced total synthesis of 1 was reported by Ratovelomanana-Vidal and coworkers (Scheme 1): [27] these authors established an elegant, short and selective route to the amine part 9 of 1 via dynamic kinetic resolution (DKR) upon ruthenium catalysed asymmetric hydrogenation of the α-amino-β-ketoester 7.…”