Studies in the claisen rearrangement. Part XII . Synthesis of benzofuro[3,2-c] [l]-6a,lla-dihydro-lla-methylbenzopyrans from 1,4-diaryloxy-2-butynes

Successful Claisen rearrangement of a number of 1,4-diaryloxy-2-butynes is reported. The products of such a rearrangement are the benzofuro[3,2-c]benzopyrans. This novel rearrangement offers a facile synthetic route to tetracyclic derivatives resembling the naturally occurring pterocarpans.     

Conformational analysis of trans-2,3-diaryloxy-1,4-dioxanes. A tool for discriminating between steric and electronic effects in the position of

The conformation of several $\text{trans}$-2,3-diaryloxy-1,4-dioxanes has been studied using ¹H NMR techniques. $\text{Trans}$-2,3-bis(4-nitrophenoxy)-1,4-dioxane and $\text{trans}$-2,3-bis(4-methoxyphenoxy)-1,4-dioxane have been found to be predominantly ( ≈98%) in diaxial conformation in CDCl₃). On the other hand, $\text{trans}$-2,3-bis(2,6-dimethylphenoxy)-1,4-dioxane exists in the same conditions as a 66:33 mixture of diaxial and diequatorial conformers. An explanation based on the fulfilment of the exo-anomeric effect is provided.     

Syntheses and thermal reactions of 2-alkyl(or aryl)-1-benzoyl-3,4-dihydro-2-thianaphthalenes

1-Benzoyl-2-methy1-3,4-dihydro-2-thianaphthalene ($\text{4a}$) underwent novel intermolecular 1,4-rearrangement in refluxing toluene to give an enol ether $\text{5a}$, while rearrangement of 2-phenyl derivative $\text{4e}$ proceeded intramolecularly in refluxing xylene to afford a 1,4-rearranged enol ether $\text{5b}$. On the other hand, ylides $\text{4a–e}$ were refluxed in alcohols to afford some ring-opened products $\text{10–12}$.     

Synthesis of 1,4-dihydropyrrolo[3,2-b]pyrrole

Dihydropyrrolo[3,2-b]pyrrole $\text{1}$ was synthesized starting from 1,4-bis(trimethylsilyl)benzene.     

Chemistry of 1,4-dioxene II : A new method for the two-carbon homologation of aldehydes and ketones to α-hydroxymethyl ketones

1,4-Dioxen-2-yl lithium $\text{2}$ reacts with ketones or aldehydes to give alcohols $\text{3}$ which lead after an allylic rearrangement under mild conditions, followed by reduction and hydrolysis to α-hydroxymethyl ketones in fair yields.     

Bis(tricarbonyliron) complexes of P-quinodimethanes: fragmentation and isomerisation under electron impact

EI mass spectra of $\text{trans}$-η⁴,η⁴-[3,6-bis(methylene)-1,4-cyclohexadiene]-bis=(tricarbonyliron) complexes $\text{1a}$, $\text{b}$ are reported. The fragmentation pathway is rationalized by assuming a rearrangement of the $\text{trans}$-bis(tricarbonyliron) complexes into the $\text{cis}$-isomers under electron impact.     

A short synthesis of 4-aryioxymethyl-δ3-chromenes and 3-(β-aryloxy)ethylbenzofurans

A direct and short route to the synthesis of 4-aryloxymethyl-δ³ -chromenes and 3-(β-aryloxy)-ethylbenzofurans is described. Hydration of I,4-diaryloxy-2-butynes with mercuric oxide and sulfuric acid affords, instead of a ketone, the cyclization product of the ketone. In three of the diaryloxy-butynes studied, the corresponding aryloxyethylbenzofurans are formed. In no instance could the ketone be isolated from the hydration reaction.     

Synthesis of 2-isopropylfuro(2,3-b)quinolines-a new synthesis of (±)-lunacrine, (±)-lunasine and (±)-demethoxylunacrine

A new and convenient synthesis of 2-isopropylfuro-(2,3-b)quinolines ($\text{4}$) from 3-(3-methylbut-1-enyl)-2-quinolones ($\text{2}$) is described. A neat synthesis of the alkaloids (±)-lunacrine ($\text{1a}$), (±)-lunasine ($\text{12a}$) and (±)-demethoxylunacrine ($\text{1b}$) is also reported.     

Pyridinethiones—II : Preparation of condensed pyridines related to 3-formyl-2(1H,-pyridinethione

Some condensed pyridines, isothiazolo[4,5-b]pyridine, 2-oxo-2$\text{H}$-thiopyranyl[5,6-b]pyridines, and thieno[3,2-b]pyridines, have been prepared from 3-formyl-2(1$\text{H}$)-pyridinethione or the 1-substituted precursors for this compound.     

Base catalysed rearrangement of 2-methyl-3,3-bisalkylthioacrylophenones to 2-alkylthiomethyl-3-alkylthioacrylophenones via mobile keto allyl intermediates

The title compounds ($\text{1a}$-$\text{e}$) undergo facile base catalysed rearrangement to give $\text{5a}$-$\text{e}$. A mechanism involving thioallylic rearrangement of intermediates, 2-bisalkylthiomethyl acrylophenones, ($\text{3a}$-$\text{e}$) has been proposed.     

Trifluoroacetic acid catalyzed and thermal rearrangement ofα- aryloxymethyl cinnamic acids.

Severalα- aryloxymethyl cinnamic acids $\text{1}$ have been rearranged in refluxing trifluoroacetic acid (TFA). The thermal rearrangement of the same acids in Polyethylene glycol - 200 (PEG - 200) has also been investigated.     

Stereoselective diels-alder reactions between 9-alkyl-1,4-dihydronaphthalen-1,4-imines and 2-alkylisoindoles

The Diels-Alder reaction between 9-alkyl-1,4-dihydronaphthalen-1,4-imines ($\text{1}$) and 2-alkylisoindoles ($\text{2}$) occurs in refluxing xylene to give exclusively the exo-endo cyclo-adducts $\text{3}$ ($\text{D}$).     

Thiophenol additions to alkenylidenecyclopropanes. A novel synthesis of karahanaenone

The additions of thiophenol to alkenylidenecyclopropanes (e.g. 3, 14) are found to be highly regioselective and stereoselective leading to $\text{endo}$- (or $\text{cis}$- vinyl sulphide adducts (e.g. 4, 15) resulting from additions to the 1,4-double bonds in the starting materials. Thiophenol addition to (1) leads to a mixture of the vinyl sulphides (16) and (17) which undergo Cope rearrangement producing the cycloheptadiene (18); hydrolysis of (18) then gives karahanaenone (19) an odoriferous constituent of Japanese hop and Cypress oil.     

Sensitized photooxygenation of β-methoxystyrene and 1-(β-methoxyvinyl)naphthalene

Single oxygen can easily add to 1-(β-methoxyvinyl) naphthalene ($\text{1}$) with retention of sterochemistry to afford a stable 1,4-endoperoxide $\text{3}$. Sensitized photooxygenation of β-methoxystyrene ($\text{2}$) gives mainly Diels-Alder adducts of $\text{o}$-formylmethide quinone ($\text{12}$) which might be derived from initially formed 1,4-endoperoxide $\text{10}$.     

Studies in claisen rearrangement - novel thermal and mercuric trifluroacetate induced transformations of 2,4-di(N-aryl)amino-1,3,5-triazin-6yl-prop-2-y

The thermal rearrangement of 2,4-di(N-aryl)amino-1,3,5-triazin-6yl-prop-2-ynyl ethers $\text{1}$ yield a mixture of 6-methyleneimidazo(1,2-a)-1,3,5-triazine-4-one $\text{6}$ and 6-methylimidazo(1,2-a)-1,3,5-triazine-4-one $\text{7}$, whereas under the influence of mercuric trifluroacetate the ethers $\text{1}$ yield only $\text{6}$, at room temperature. Mechanisms invoking [3,3] sigmatropic rearrangement of ethers $\text{1}$ were proposed to account for the product formation.     

Rearrangement spinal en serie a/b cis : conversion du lithocholate de methyle en derives du d-homoandrostane

A new backbone rearrangement is observed in A/B $\text{cis}$ methyl lithocholate derivatives. It is initiated from the C-3 carbon either by dehalogenation of the chloroesters $\text{1}$ by AgSbFg₆ or by the action of the triflic anhydride on the si1y1ated ether $\text{2}$. This rearrangement leads to methyl diacholenate $\text{3}$ and new lactones in D-homoandrostane series $\text{5}$ and $\text{6}$. The differences of behaviour between A/B $\text{cis}$ and A/B $\text{trans}$ series and the mechanism of rearrangements are discussed.     

Synthesis of erythrinin A,a naturally occurring pyranoisoflavone

Erythrinin A ($\text{10}$) has been synthesised by the oxidative rearrangement of dihydropyranochalcone $\text{1}$ with thallium(III) nitrate (TTN) in trimethyl orthoformate (TMOF) to the dimethyl acetal $\text{2}$, followed by cyclisation to $\text{3}$, demethylation to $\text{6}$ and dehydrogenation. Compound $\text{10}$ could also be obtained from chalcone $\text{4}$ on similar rearrangement followed by cyclisation, demethoxymethylation and dehydrogenation. In another route, chalcone $\text{7}$ was oxidatively rearranged with TTN in TMOF, to $\text{8}$ which on treatment with HCl yielded $\text{10}$.     

Mercuric ion-catalyzed hydration of derivatives of 1,4-dichloro-2-butyne. Hydration of 1-aryloxy-4-arylthio-2-butynes, 1,4-bis(arylthio)-2-butynes,and 1,4-bis(arylsulfonyl)-1-butynes

The mercuric ion-catalyzed hydration of 1,4-bis(arylthio)-2-butynes and 1-aryloxy-4-arylthio-2-butynes was studied. The 1,4-bis(arylsulfonyl)-2-butynes afforded 1,4-bis(arylsulfonyl)-2-butanones (7). The 1,4-bis(arylthio)-2-butynes afforded a variety of products in acetic acid among which were: 1,4-bis(arylthiomethyl)vinyl acetate ( 18 ); 1,4-bis(arylthio)-2-butanone ( 15 ); 1-(arylthio)-3-buten-2-one ( 16 ); and 1-(arylthio)-4-acetoxy-2-butanone ( 17 ). Ketone 15 eliminates arylthiol in an acidic medium yielding 16 which undergoes Michael addition of solvent to give 17. Treatment of 7 with base in the presence of a nucleophile (ArSH) analogously leads to elimination of arylsulfinic acid, followed by Michael addition of arylthiol. Hydration of 5 in methanol cleanly gave 1-(arylthio)-4-methoxy-2-butanones ( 19 ). In contrast, 1-aryloxy-4-arylthio-24)utynes afforded chromenes ( 8 ) by intramolecular cyclization. No thiochromenes were formed in any of the examples investigated.     

Synthesis of ansamycins: An approach to the naphthoquinone portion of the rifamycins and streptovaricins

Naphthoquinone $\text{1}$, a fully functionalized model for intermediates in ansamycin synthesis, was prepared by the intramolecular Claisen condensation of benzofuran $\text{9}$ followed by oxidation of the novel tricyclic compound $\text{10}$.     

Nouvelle synthese stereoselective de disels de botadiene-1,3 ylene-1,4 bisphosphoniums

A new way to 1,4 butadienylene bisphosphonium salts $\text{2}$ is given, using a base-catalyzed double isomerization process on acetylenic precursors $\text{3}$. The precursor can be synthetized by nucleophilic substitution of 1,4-diiodo 2-butyne with triphenylphosphine. The selection of the 1,4-dihalo 2-butyne has a strong influence on the course of the reaction which, besides that, can lead to exclusive formation of a new stabilized ylid-disalt $\text{5}$.The stereoselectivity of the t.butylamine induced double isomerization allows the isolation of the kinetic product, the (Z, E) 1,4-butadienylene bisphosphoniun salt, which is then readily converted into the more stable (E, E) isomer.