Baldur Föhlisch

Regioselektive [4+3]-cycloadditionen von heterosubstituierten allylium-2-olaten (oxallylen) an 2-methylfuran

Abstract 1,1-Dichloro- and 1,3-dichloro-2-alkanones react with 2-methylfuran in the presence of lithium perchlorate/triethylamine to form 2-chloro-1-methyl-8-oxabicyclo [3.2.1]oct-6-ene-3-ones predominantly.

Total synthesis of racemic lasidiol via intramolecular [4+3] cycloaddition

Lasidiol, a sesquiterpenoid with a carotane skeleton, and its 8a-epimer have been synthesized in 12 steps starting from 2-methylfuran. Key elements in the synthesis are constructions of the carbon framework in an intramolecular [4+3] cycloaddition and cleavage of the epoxy-bridge by reductive elimination with sodium naphthalenide after reduction and hydrogenation of the bromo-substituted cycloadducts.

Cycloaddition of Acyclic Conjugated Dienes with a Tetrachloro‐Substituted Oxyallyl Intermediate Generated from Pentachloroacetone

Pentachloroacetone (1) reacts with several conjugated dienes in the presence of sodium trifluoroethoxide/trifluoroethanol to form cycloadducts of a tetrachlorooxyallyl intermediate 6, mainly in the [4+3] mode. Representative [4+3] cycloadducts, i.e. α,α,α′,α′-tetrachlorocycloheptenones 9, have been dehalogenated and dehydrohalogenated, furnishing α,α′-dichlorotropones 15 in high yields.

Erzeugung und cycloaddition von allyliumionen aus α-halogenketonen unter solvolyse-bedingungen

Abstract Some α-haloketones react with furan in methanolic solution in the presence of base to form the 3-oxo-8-oxabicyclo[3.2.1]oct-6-enes ( 11 ), the products derived from a [4+3] cycloaddition of an allylium intermediate ( 5 or 6 ).

Baseninduzierte Umlagerungen von 3,9-Dioxatricyclo[3.3.1.02,4]nonan-7-onen zu m-Hydroxyphenylcarbonyl-Verbindungen

Zusammenfassung Durch [4+3]-Cycloaddition leicht zugangliche 8-Oxabicyclo[3.2.1]oct-6-en-3-one ( 5 ) wurden an der CC-Doppelbindungepoxidiert. Die gebildeten 3,9-Dioxatricyclo[3.3.1.0 2,4 ]nonan-7-one ( 6 ) lagerten sich bei der Behandlung mit ethanolischem Natriumethoxid in guten Ausbeuten zu 3-Hydroxybenzaldehyden ( 8a-d ) und 3-Hydroxy-2,4,5-trimethylacetophenon ( 8e ) um. Als Zwischenstufen dieser Umlagerungen werden 8-Hydroxy-6-oxatricyclo[32.1. 02,7 ]octan-3-one postuliert; das Trimethyl-Derivat 7g und die 6-Carba-Derivate 4a,b konnten isoliert werden.

BILDUNG UND SPALTUNG VON 3-THIETANON

Abstract 3-Thietanone (3a) reacts rapidly with methanolic sodium hydrogen sulfide to form a mixture of products wherein 2,4-dimethylthiophene-3-thiol (9), the corresponding disulfide (10) and 3,6-dimethyl-7-oxa-2,5-dithiabicyclc [2.2.1]-heptane (7) could be detected. These products are explained to be derived from the unstable 1-mercapto-2-propanone (5) formed by reductive cleavage of the thietanone ring. The cleavage is postulated to occur by attack of hydrogensulfide ion at the ring sulfur. 3-Thietanone can be synthesized from 3-thietanol by oxidation with dimethyl sulfoxide/benzoic acid anhydride. 3-Thietanon (3a) reagiert rasch mit methanolischem Natriumhydrogensulfid zu einem Produktgemisch, in dem 2,4-Dimethylthiophen-3-thiol (9), das entsprechende Disulfid (10) und 3,6-Dimethyl-7-oxa-2,5-dithiabicyclo [2.2.1]-heptan (7) nachgewiesen werden konnten. Diese Produkte lassen sich aus dem instabilen 1-Mercapto-2-propanon (5) ableiten, welches durch reduktive Spaltung des Thietanon-Ringes gebildet wird. F...

Cleavage of the oxygen bridge in 8-oxabicyclo[3.2.1]octanes by reductive elimination

Abstract Several 2(4)-bromo- or chloro-8-oxabicyclo[3.2.1]oct-6-en-3-ones (2), available by [4+3] cycloaddition of monohalogeno-oxyallyl intermediates with furans, were reduced to halogenated 8-oxabicyclo[3.2.1]oct-6-en-3endo-ols (6) and saturated analogues (7). Cycloheptene-1,3trans-diols (8,11) were formed preferentially by reductive elimination.

Base-Induced Solvolyses of [3.2.1]Bicyclic α,α′-Dichloro Ketones − 1,3-Transposition and Ring-Contraction

2,4-Dichlorobicyclo[3.2.1]oct-6-en-3-one (1) and its spirocyclopropane (4) and 8-oxa analogues (15, 16) react with methanolic sodium methoxide to furnish bicyclic α-oxo-acetals (3b, 5b, 17, 18) through an enolization/ionization mechanism. With trifluoroethanol/sodium trifluoroethoxide, the corresponding trifluoroethyl acetals (3a and 5a) are formed. Basic hydrolysis affords 2-endo-hydroxynorbornene-2-exo-carboxylic acid (20x) and the 7-oxa analogues (22x, 23x), presumably through benzilic acid rearrangement of the α-diketones.

A critical examination of the preparation of polychlorinated acetones

INTRODUCTION ...................................................................................................................... 551 RESULTS AND DISCUSSION ................................................................................................ 553 1 . Mechanistic Considerations ............................................................................................... 553 2 . Calculations ......................................................................................................................... 554 3 . ExperimentaI Results .......................................................................................................... 558 4 . 1.1.1. 3.Tetrmhlometone (1.1.1. 3.TeCA) ....................................................................... 559 5 . 1.1.3. 3.Tetrmhloroacetone (TeCA) ................................................................................... 560 6 . Pentachloroacetone ............................................................................................................. 562 7 . Waste Disposal . Hexachlometone ................................................................................ 562 CONCLUSIONS ......................................................................................................................... 563 EXPERIMENTAL SECTION .................................................................................................. 563 REFERENCES ............................................................................................................................ 568

4-Methyl-N-(3-oxo-8-oxabicyclo[3.2.1.]oct-6-en-1-ylmethyl)-benzenesulfonamide

Zinc powder (10.6 g, 160 mmol) was given to an ice-cold solution of methanol (40 mL) saturated with ammonium chloride.[...]