Iris Klein

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 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.

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.

Diastereoselective synthesis of tricyclo[3.2.1.02,7]octanes; chiral building blocks for terpenes

One pot cascade reactions of 3-benzyloxy-cyclohex-2-enone (1) with tert-butyl-(Z)-(+)-2-chloro-3-[(4S)-2,2-dimethyl-1,3-dioxolan-4-yl]-2-propenoate (2) lead to (1S;2R;5S;7S;8R;4′S)-tert-butyl-2-benzyloxy-8-(2′,2′-dimethyl-1′,3′-dioxolan-4′-yl)-6-oxo-tricyclo[3.2.1.02,7]octane-1- carboxylate (3) and with (E)-(+)-2 to (1R;2S;5R;7R;8S;4′S)-4. The tricyclic compounds 3 and 4 were formed with high diastereomeric excess.

Highly Functionalized Bicyclo[3.2.1]octane Derivatives from Readily Available 2′‐Alkoxytricyclo[3.2.1.02,7]octanes: Building Blocks for Terpenes, Part I

2′-Alkoxytricyclo[3.2.1.02,7]octanes 4-R are obtained in good to excellent yields from methyl 2-chloro-2-cyclopropylideneacetate (3) and the dienolates derived from the 3-alkoxycyclohex-2-enones 1-R and 2-R, by a cascade of two consecutive Michael additions and a γ-elimination. Compounds 4-R are transformed to the correspondingly substituted bicyclo[3.2.1]octanecarboxylates 5 by treatment with acid. 2′-Methoxytricyclooctanes 4a−d-Me are readily deprotonated to give chelation-stabilized cyclopropyllithium derivatives 6-Me, which react with electrophiles to yield the 7′-substituted tricyclo[3.2.1.02,7]octanes 4f−i-Me (61−66%). By acidic workup of such reaction mixtures, or subsequent treatment of the isolated products 4f−i-Me with acid, efficient transformation to the correspondingly substituted bicyclo[3.2.1]octanecarboxylates 5 is observed.

Synthesis and reactions of chiral 5-substituted (Z)-ethyl 2-bromo-3-(1,3-dioxolan-4-yl)-2-propenoates

Abstract Wittig olefination of the aldehydes 2a/b gave the 2-bromo-dienes 3a/b . Regioselective catalytic Sharpless asymmetric dihydroxylation (AD) led to the diols 4a/b with high enantiomeric excess (ee > 94 %). Cascade reactions of 5a/b with dienolate 6 yielded 7a/b with excellent diastereomeric excess (de > 95 %).

A Short Synthesis of the New Vallesiachotamine Lactone from Cephaelis dichroa (Standley)

Abstract The new vallesiachotamine lactone (1) is synthesized from lactone 5aby selenium mediated dehydrogenation. Lactone 5a was previously prepared from deprotonated butyrolactone Li-4 and the pyridinium salt 3 (Wenkert reaction).