Hydroboration d'amines insaturees: III - Reactions anormales d'hydroboration-alkylation d'amines propargyliques bromees

By hydroboration-alkylation of brominated propargylamines, we obtain brominated ethylenic amines and not the expected ethylenic amines with thexylalkylboranes. The thexyl group shows, in all cases, an anomalous high migratory aptitude.     

Synthese univoque d'amines tertiaires insaturees par voie organometallique a partir de sels d'immonium : II. Synthese d'amines β- et α-ethyleniques

In this work, the best method to prepare unequivocally and in good yields β-and α-ethylenic tertiary amines: RR′CHNR″₂ (R unsaturated group, R′, R″ alkyl groups), from immonium salts, has been evaluated.     

Hydroboration d'amines insaturees—II: Régio et stéréosélectivité de l'hydroboration-alkylation d'amines acétyléniques

The hydroboration reaction of acetylenic amines R¹R²NCH(R³)CCR⁴ was studied. We report the first results of a study of the reactivity of dialkylborane R₂BH towards these amines which allow us to propose a new method for the synthesis of differently substituted β-ethylenic amines. The regioselectivity and the stereoselectivity of this reaction are examined and allow us to set out the possibility of a trans hydroboration.     

Substitutions allyliques : Nouvelle voie d'accès aux amino-2 didésoxy-2,3 hexopyrannoses synthèse d'un derivé de la tobrosamine

Synthesis of the methyl α-D-glycoside of N,N-diacetyl tobrosamine 16 from methyl α-D-mannoside 3 is described. Selective introduction of an azido function at C-6 cave 4. Regio- and stereospecific ring opening of benzylidene derivative 7, after O-methylation, afforded 8. Elimination of bromine followed by O-debenzoylation on C-2 led to enose 10. Azidolysis of 10 by means of alkoxyphosphonium salt (triphenylphosphine, diethylazodicar-boxylate and N₃H) gave 12 with high stereoselectivity. Reduction, acetylation and acid hydrolysis furnished N,N-diacetylbrosamine. Alternative way to 13, epimeric 2-amino derivative of 14, is also described.     

Cyclodeshydration d'alcool-phenols induite par l'h.m.p.a. nouvelle voie d'acces aux dihydrobenzofurannes et dihydrobenzopyrannes

Substituted benzodihydrofurans and benzodihydropyrans 2 were obtained by heating alcohol-phenols 1 in HMPA. New cyclic alkyl phenyl dimethylaminophosphoramidates 3 were also isolated. Their thermolysis was studied. This and other considerations show that bis(dimethylamino)phenol alkyl phosphorodiamidate 4 and by-product 3 are intermediates of an alternative two or threestep reaction pathway. This mechanistic study gave indications on choice of best experimental conditions for this new cyclodehydration method.     

Azidomercuration-demercuration : voie d'access aux amino-sucres

An improved method of azidomercuration with mercuric trifluoroacetate is described. Applied to unsaturated carbohydrates it provides a high yield synthesis of aminosugars. In the example herein reported, 80% regioselectivity and total stereospecificity are obtained.     

Acyloxyalkylidènephosphoranes—II : Etude des ω-acyloxy n-butylidènetriphénylphosphoranes. Nouvelle voie d'accès aux dihydro-3,4 2h-pyrannes

ω-Acyloxy n-butylidenetriphenylphosphoranes give α-acyl n-butylidenetriphenylphosphoranes by intermolecular condensation in t-BuOH, and 3,4-dihydro-(2H)-pyrans by intramolecular condensation in toluene. The α-acyl n-butylidene phosphoranes, which are the tautomeric form of α-acyloxaphosphanes, do not lead to cyclobutylketones but to dihydropyrans.     

Alcaloides steroidiques—CLXXI : Nouvelle methode d'acces aux 4H dihydro-5,6 oxazine-1,3

Access to 4H 5,6-dihydro 1,3-oxazine by nitrogen insertion into a 2-hydroxy or 2-methoxytetrahydrofuran is described. A reaction mechanism is proposed.     

Nouvelle voie d'accès aux isochromènes

Reaction of monophosphonium salt derived from α,α-dibromo-o-xylene with sodium carboxylates, followed by action of base, gives isochromenes.     

Nouvelle voie d'acces aux dihydro-3,4-2H-benzoxazines-1,3

3,4-Dihydro-2H-1,3-benzoxazines were prepared from primary amines and dihalocompounds by a method which can lead to compounds dissymetrically substituted in positions 2 and 4.     

Ouverture d'epoxydes par des acides organiques dans L'H.M.P.T.: nouvelle voie d'acces a des desoxypentopyranosides

The opening of pyranic epoxides with organic acids in HMPA leads to regioselectively esterified methyl deoxy$\text{threo}$pentopyranosides; one of them is a convenient intermediate to provide $\text{erythro}$ isomers.     

Acyloxyalkylidènephosphoranes—III : Etude des ω-acyloxybenzylidènetriphénylphosphoranes.nouvelle voie d'accès aux benzofurannes

The intramolecular condensation of o-acyloxybenzylidenetriphenylphosphoranes leads to acylated products in t-BuOH and to benzofurans in toluene. Mechanistic aspects are discussed. A general method is described for the synthesis of benzofurans from o-cresols, o-hydroxybenzylic alcohols, and deactivated phenols.     

Voie d'acces aux benzylidene-1 cyclohexadiene-2,4 fer tri-carbonyle et autres composes apparentes. Stabilisation singuliere d'une forme tautomere d'un aromatique

2,4-Cyclohexadien-1-yldimethylphenylphosphonium tetrafluoroborate obtained from the reaction of 2,4-cyclohexadien-1-yltricarbonyliron with PMe₂Ph in 96% yield, reacts readily with benzaldehyde in the presence of base to give 1-benzylidiene-2,4-cyclohexadienetricarbonyliron in 90% yield; this and other related reactions provide the first examples of the Wittig reaction adjacent to a tricarbonyl moiety.