Dietrich Spitzner

Akzeptoren für die doppelte Michael-reaktion, eine verbesserte synthese von cyclopropylidencarbonsäureestern und deren reaktivität gegenüber cyclohexadienolaten

Abstract Ethyl cyclopropylidene acetate and analoges are prepared in good yield by an acid catalyzed Wittig reaction. They are used as equivalents of senecioic acid esters in the aprotic double Michael reaction to give spirocyclopropyl substituted bicyclo[2.2.2] octanes.

ON THE STRUCTURE OF OXYBLEPHARISMIN AND ITS FORMATION FROM BLEPHARISMIN

Abstract The blepharismins ( 1 ) from Blepharisma japonicum give the corresponding oxyblepharismins ( 2 ) on irradiation in vitro and in vivo . The chemical structures of these compounds are elucidated and a mechanism is given for this unusual transformation.

Facile construction of terpenoid frameworks by cycloadditions with methyl 2-chlorocyclopropylidenacetate

Abstract Methyl 2-chlorocyclopropylidenacetate (2-Cl) smoothly [2+4]cycloadds to cyclopentadiene and 2,3-dimethylbutadiene at room temperature. With the donorsubstituted cyclohexadienes 6, 9 at elevated temperatures (60, 120°C respectively) 2-C1 reacts without any observable regioselectivity. In contrast, 2-Cl, when treated with lithium cyclohexadienolates 13 undergoes completely regioselective iterative Michael additions with subsequent intramolecular γ-elimination to give tricyclic γ-ketoesters 16 in good to excellent yields. The products 16 can readily be transformed to multifunctional bicyclo[2.2.2]octane as well as bicyclo [3.2.1]octane derivatives 17. A rationalization of the unprecedented reactivity of 2-Cl on the basis of its available structural features (IP(π), 1JC,C, CC bond length) is offered.

Facile synthesis of highly functionalized bicyclo[3.2.1]octanes as potential building blocks for various natural products

Abstract The cascade cycloaddition of 1-alkoxycyclohexadienolates 2 onto 2-chloro-2-cyclopropylideneacetate 4 yields 2-alkoxytricyclo[3.2.1.0 2.7 octane-2,6-diones 8 under acid catalysis. The tricyclooctanones 7 can be further elaborated, e. g. by Wittig olefination and reduction of the carbonyl group, or deprotonation at the bridgehead C-7 with subsequent alkylation, acylation or aldol reaction, before they are rearranged to the highly functionalized bicyclo[3.2.1]octane derivatives 10 , 11 , 13 , and 17 , respectively. The diones 8 can also be further manipulated, e. g. by regioselective Wittig olefination at C-2.

Diastereoselective synthesis of bicyclo[2.2.2]octanes by double Michael addition

Abstract Several chiral acrylates (7b–f) react with kinetically controlled generated lithium dienolate 6a to form chiral bicyclo[2.2.2]octanes 4 with modest d.e.. It was found, that the diastereoselection is improved, when the corresponding trimethylsilyl ether 6b reacts with chiral acrylates under Lewis acid catalysis. The absolute stereochemistry of these bicyclo[2.2.2]octanes was determined by X-ray analysis.

Investigations into acrylamide precursors in sterilized table olives: Evidence of a peptic fraction being responsible for acrylamide formation

Formation of acrylamide from commercial model peptides containing protein-bound aspartic acid, alanine and methionine, respectively, at 200°C and different times in the absence of any carbonyl sources, was demonstrated by HPLC-MS/MS analyses. Further experiments using a more complex model system based on olive water, i.e., the aqueous fraction of olive pulp from untreated and lye-treated green olives, were performed. After partial fractionation of olive water by solid-phase extraction, only peptides/proteins containing fractions, being devoid of free asparagine, generated significant amounts of acrylamide during less harsh heat treatment (121°C for 30min). In contrast, acrylamide was not detected after heating the same fraction under identical thermal conditions when previously subjected to acid hydrolysis. Consistently, significant amounts of acrylamide were released after heating the albuminous precipitate resulting from acetone precipitation of olive water. These results strongly support the role of peptides/proteins as precursors of acrylamide formation in sterilized olives.

Short total synthesis of the spiro[4.5]decane sesquiterpene (−)-gleenol

Abstract The spirocyclic sesquiterpene (−)-gleenol was prepared in five steps starting from (−)-methone via a di-olefin. The final spiro-ring system was made using the olefin metathesis reaction. The resulting ketone was selectively reduced to the natural product.

Anionically induced domino reactions; synthesis of analogues of marine sesquiterpenes

Abstract An anionically induced domino reaction is the key step in the synthesis of the isotwistane skeleton. This precursor can be transformed into the marine sesquiterpene 2-isocyanopupukeanane or its structural analogues.

Amethystin, the Coloring Principle of Stentor amethystinus

Among the ciliates, Stentor amethystinus stands out for its conspicuous red-violet color compared to its blue- and red-colored relatives Stentor coeruleus and Blepharisma japonicum. Rich blooms in German lakes allowed us to collect sufficient organisms to isolate the pigments and elucidate the structure of the main component amethystin (4) by spectroscopic methods as a carboxy derivative of blepharismin. Depending on conditions, the carboxy group appears as an orthoester or as a mixture of the orthoester and small amounts of a hydroxylactone. Derivatives of both isomeric forms were obtained by acetylation and methylation supporting the proposed structures. On reaction of amethystin with base in the presence of oxygen, oxyamethystin and, under vigorous conditions, p-hydroxybenzoic acid were formed. In addition to 4, two homologues, an isomer of amethystin, and stentorin F (1b) were identified in the primary extract. Further, a biosynthetic scheme is proposed linking stentorin, blepharismin, and amethystin type compounds to the hypothetical protostentorin as a common intermediate.

Synthesis and Anionically Induced Domino Reactions of Chiral α‐Bromo α,β‐Unsaturated Esters

The chiral α-bromo α,β-unsaturated esters 3 and 9 are prepared by asymmetric Sharpless dihydroxylation (AD) of 5 and from ester 7 and the chiral diols 8 by transacetalization, respectively. Both types of α-bromo α,β-unsaturated ester react with the kinetic lithium dienolates of enone 10 to give functionalized tricyclo[3.2.1.02,7]octanes 11. Esters 3 give one single diastereomer (de ≥ 95%), whereas mixtures of diastereomers (de 28 to 46%) are obtained with the esters 9.