Acyclic stereoselection. Part 42. 1,4- and 1,5-Stereoselection by sequential aldol addition to a .alpha.,.beta.-unsaturated aldehydes followed by Claisen rearrangement. Application to total synthesis of the vitamin E side chain and the archaebacterial C40 diol

Abstract

ChemInform Abstract Aldol reaction of the silylated ketone (I) with the α,β-unsaturated aldehyde (II) yields the adduct (III) which is subjected to the Claisen rearrangement reaction, forming 1,4-stereoselectively the ketone (V). 1,5-Stereoselection is achieved in the rearrangement of the acylated aldol adduct (X), obtained by monoprotection of the diol (VI) with tert-butyldimethylsilyl chloride (VII), followed by acylation of the alcohol (VIII) with propionyl chloride (IX). (X) gives either the 2,6-syn acid (XI) via the corresponding E-enolate or the 2,6-anti acid (XII) via an intermediate Z-enolate. Numerous further examples are given in the original paper.

The Epoxy‐Ramberg–Bäcklund Reaction (ERBR): A Sulfone‐Based Method for the Synthesis of Allylic Alcohols

“…Following a slightly different approach, the α-methyl epoxide 4t was prepared as a 1:1 mixture of diastereomers from trans-4k following lithiation and quenching of the resultant anion with MeI. [33] Treatment of this mixture with LiOtBu (2 equiv.) gave the tetrasubstituted allylic alcohol, which was converted into the acetate 16 to facilitate the chromatographic separation from the remaining starting material 4t.…”

Membrane-spanning lipids for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer

“…Fig. 1A shows an example of caldarchaeol with two cyclopentane rings and the stereochemistry as published ( 38,40,41 ). Under our culture conditions, caldarchaeols with one to three cyclopentane rings were predominant.…”

“…The nomenclature for derivatives of caldarchaeols used throughout this paper follows published recommendations ( 53,54 ). The confi guration of caldarchaeol as shown here was deduced previously mostly by chemical methods ( 24,38,40,41,55 ). As isocaldarchaeols and caldarchaeols just differ in a parallel versus antiparallel arrangement of their two glycerol moieties, respectively, it was not possible to separate them.…”

Determination of the Configuration of an Archaea Membrane Lipid Containing Cyclopentane Rings by Total Synthesis

“…[4] In fact, the configuration of the macrocyclic tetraether A has been determined by total synthesis of the diol C and comparison with a sample of C obtained by degradation of natural A. [5] In the meantime, a synthesis of A has also been carried out. [6] In contrast, the configurations of the compounds containing five-membered rings are largely unknown and, as a consequence, stereoselective synthesis of a lipid containing cyclopentane units has not been undertaken.…”