Jose Galindo

A New Variant of the Claisen Rearrangement from Malonate-Derived Allylic Trimethylsilyl Ketene Acetals: Efficient, Highly Enantio- and Diastereoselective Syntheses of (+)-Methyl Dihydroepijasmonate and (+)-Methyl Epijasmonate.

Complete chirality transfer occurs in the smooth Claisen rearrangement of the trimethylsilyl (TMS) ketene acetals, which were prepared from allylic malonates (R)-1 (R=pentyl, 2-(Z)-pentenyl). These are in turn accessible by enantioselective reduction/esterification or by enzymatic kinetic resolution. The cis configuration in (+)-3 was achieved by highly syn-selective epoxidation of (+)-2, followed by suprafacial 1,2-H migration.

Synthesis of (-)-Vulcanolide by enantioselective protonation

Two efficient enantioselective syntheses of the more active (S,S)-enantiomer of the powerful musk odorant Vulcanolide are described. In both syntheses, the key step is an enantioselective protonation of a ketone enolate. A third enantioselective protonation, of a thiol ester enolate, was applied for the determination of the absolute configuration of Vulcanolide by comparison with a known compound.

Diastereocontrolled synthesis of functionalized transdecalins via electrocyclic reaction of trienol ethers

(E)-Trienol silyl ethers 10 and 11, selectively, prepared by mono-Grignard reaction on methyl β-cyclogeranate (7) or by deprotonation of enone 8 were transformed to trans-decalins 5 and 6 by a thermal electrocyclic reaction. The hitherto unknown enones 5 and 6 exhibit interesting organoleptic properties and show promise as versatile synthetic intermediates. The herein described transformation opens a new route for the direct construction of C(6)-functionalized drimanes such as cinnamodial (3) and forskolin (4).

Eine neue Variante der Claisen-Umlagerung von aus Allylmalonaten abgeleiteten Trimethylsilylketenacetalen – effiziente, hoch enantio- und diastereoselektive Synthesen von (+)-Methyldihydroepijasmonat und (+)-Methylepijasmonat

Mit vollstandiger Chiralitatsubertragung verlauft die Claisen-Umlagerung der Trimethylsilyl(TMS)-Ketenacetale, die aus den Allylmalonaten (R)-1 (R=Pentyl, 2-(Z)-Pentenyl) hergestellt wurden. Diese sind ihrerseits durch enantioselektive Reduktion/Veresterung oder durch enzymatische kinetische Racematspaltung zuganglich. Die cis-Konfiguration in (+)-3 wurde durch eine hoch syn-selektive Epoxidierung von (+)-2 und eine anschliesende suprafaciale 1,2-H-Wanderung sichergestellt.

New triene synthesis from sorbic acid: two-step synthesis of cis- and trans- galbanolenes

Abstract The lithium dianion of sorbic acid reacts with hexanal at the C(2)-position to afford separable anti - and syn-hydroxy carboxylic acids 3 and 4 (87%; 3 4 =59:41 or 79%; 3 4 =16:84), whose stereospecific anti-decarboxylative elimination respectively affords (3E, 5Z)- and (3E, 5E)-1,3,5-undecatriene (1) and (2) (cis- and trans-galbanolenes (1 and (2) (69%). An alternative route to 1 involves conversion of 3, 4 to cis-lactone 7 (45% after chromatography) followed by thermal syn-decarboxylation (81%). The described procedure is both new and of general applicability, as illustrated by the synthesis of trienes with different substitution pattern.