Analyse Conformationnelle en Serie Alcoylidene-5 Dioxanne-1,3

Some 5-alkylidene 2-alkyl 1,3-dioxans have been studied by NMR. Analysis of the spectra leads to the conclusion that these derivatives are predominantly in the chair form, the alkyl substituent on carbon 2 being in the equatorial position. In the case of 5-alkylidene 1,3 dioxans unsubstituted at carbon 2, there is a rapid ring inversion with a very low energy barrier.     

Synthesis and structure of 1-methyl-2,3-dihydro-1,2,4-triazolium salts and their free bases

1-Methyl-2,3-dihydro-1,2,4-triazolium iodides can be obtained by reacting methylhydrazones with S-methylthioamide hydriodides, by condensing 2-methylamidrazone hydriodides with aldehydes and ketones, or by reacting methyl iodide with 1-alkylidene (or arylidene)benzamidrazones. In solutions these salts are capable of undergoing tautomerism to 1-alkylidene(or arylidene)-2-methylamidrazone hydriodides. The influence of the structural factors on the position of the tautomeric equilibrium has been studied. The free bases obtained by neutralization of the respective salts by an alkali metal hydroxide are heretofore undescribed 1-alkylidene(or arylidene)-2-methylhydrazidoimines or 4-triazolines, depending on their structure. Under the action of oxygen, these compounds are readily oxidized to substituted 1-methyl-1,2,4-triazoles with heating.Translated from Khimiya Geterotsiklicheskikh Soedineniii, No. 10, pp. 1415–1421, October, 1984.     

2-Alkylidene oxetanes by stereospecific elimination of mesylates

α-Mesyloxyoxetanes undergo stereospecific elimination to 2-alkylidene oxetanes upon treatment with potassium t-butoxide.     

Yb(OTf)3-catalyzed reactions of 5-alkylidene Meldrum's acids with phenols: one-pot assembly of 3,4-dihydrocoumarins, 4-chromanones, coumarins, and chromones

[reaction: see text] The Yb(OTf)3-catalyzed annulation reactions of phenols with 5-alkylidene Meldrum's acids enabled the synthesis of structurally diverse heterocycles in high isolated yields. A series of 4-substituted 3,4-dihydrocoumarins, 2,2-disubstituted 4-chromanones, coumarins, and 2-substituted chromones were readily and efficiently assembled, including the naturally occurring coumarins citropten, scoparone, and ayapin. Addition of phenols to biselectrophilic 5-alkylidene Meldrum's acids proceeded through two distinct multibond-forming modes: Friedel-Crafts C-alkylation/O-acylation and Friedel-Crafts C-acylation/O-alkylation. The regioselectivity of the catalytic annulation reaction was controlled by the degree of substitution on the alkylidene moiety.     

Nucleophilic 5-endo-trig cyclization of 2-(trifluoromethyl)allylic metal enolates and enamides: Synthesis of tetrahydrofurans and pyrrolidines bearing exo-difluoromethylene units

Ketones and imines bearing a 2-(trifluoromethyl)allylic moiety successfully underwent nucleophilic 5-endo-trig cyclization via their metal enolates and enamides. O- or N-Cyclization proceeded exclusively in each case to afford the corresponding five-membered heterocycles with both exo-difluoromethylene and exo-alkylidene units. On treatment with potassium hexamethyldisilazide (KHMDS) or lithium diisopropylamide (LDA), 2-(trifluoromethyl)allylic ketones or imines provided the corresponding tetrahydrofurans or pyrrolidines bearing a Z-alkylidene group with perfect or substantial stereoselectivity, respectively.     

Synthesis of indolylalkylphosphonates and 3-(1-diphenylphosphinoalkyl) indoles by reaction of 3-(1-arylsulfonylalkyl) indoles with phosphorus derivatives

Dialkyl phosphites as well as diphenylphosphine react with 3-(1-arylsulfonylalkyl) indoles under basic conditions leading to a formal substitution of the arylsulfonyl group through a reactive 3-alkylidene indole intermediate.     

钯催化剂于外向环双键立体选择合成上之应用

此报告描述钯配合物催化分子内嵌入相邻不饱和配位体及伴随之交叉偶合反应应用于各种立体选择外向环双键上之合成。亦叙述一种通用之高度位置及立体选择性α-亚烷基-γ-内酯合成法。     

Direct conversion of β,γ-unsaturated esters into lactones induced by TMS-I

β,γ-unsaturated esters readily prepared by photodeconjugation are converted in one step into butanolides by treatment with TMS-I. The reaction has been extended to the access to -alkylidene lactones.     

Syntheses of stereodefined β-alkylidene-γ-lactones and substituted β, γ-unsaturated δ-lactones

1-Trimethylsilyl-1,3-diyne derived trans-bis(trimethylstannyl) enynes undergo stepwise transmetallation with methyllithium to furnish the corresponding enynyllithium reagents. The application, in various orders, of a sequence of transmetallation-protonation-alkylation-hydroxyalkylation-hydroboration-oxidation reactions provides a novel approach to stereo-defined β-alkylidene γ-lactones and β, γ-unsaturated δ-lactones.     

Synthesis of functionalized THF and THP through Au-catalyzed cyclization of acetylenic alcohols

ω-Acetylenic alcohols are regio- and stereo-selectively converted to the corresponding α-alkylidene oxygenated heterocycles in the presence of catalytic amounts of AuCl and K₂CO₃.     

Novel Sulfamic Acid–Promoted Synthesis of 3-Alkylidene Indolone Derivatives in the Presence of Aniline via One-Pot Multicomponent Reaction

A sulfamic acid–catalyzed synthesis of 3-alkylidene indolone derivatives by addition of dialkyl acetylenedicarboxylate to isatin derivatives in the presence of aniline is reported. The reaction sequence consists of an initial Michael addition of aniline to dialkyl acetylenedicarboxylate, followed by aldol-like reaction with isatin, and then elimination of aniline to afford the product.     

Dichroisme circulaire d'olefines VI alkylidene-17 androstanes

The Cotton effect of 17-alkylidene (5α) androstanes is discussed. The large variations observed in the C.D. values indicated that the role of olefin torsion in the ground state is not significant. A semi quantitative approach based on A.B.P. model is suggested.     

Reactions SRN1 en serie heterocyclique: IV: Reactivite des sels du dimethyl-2,2 nitro-5 dioxanne-1,3

2-Alkyl 2-nitro 1,3-propanediol, 2-alkylidene 1,3-propanediol and 2-dialkylidene 1,3-propanediol are prepared via S_RN1 reactions with salts of 2,2-dimethyl 5-nitro 1,3-dioxane and acid-catalyzed cleavage of the resulting acetals.     

An acid-promoted novel skeletal rearrangement initiated by intramolecular ipso-Friedel-Crafts-type addition to 3-alkylidene indolenium cations

An acid-promoted novel skeletal rearrangement is described. Using trifluoroacetic acid as the acid promoter, an intramolecular ipso-Friedel-Crafts-type addition of phenols to 3-alkylidene indolenium cations, formation of iminium cations through rearomatization of the spirocyclohexadienone units, and intramolecular Pictet-Spengler reaction proceeded sequentially, producing tricyclic indole derivatives.     

An efficient synthetic route to functionalized δ-lactams

This paper describes a convenient synthesis of disubstituted functionalized δ-lactams based on Michael addition of primary amines to dimethyl-E-2-alkylidene glutarates 2 followed by an intramolecular cyclisation.     

An allenic Pauson-Khand-type reaction: a reversal in pi-bond selectivity and the formation of seven-membered rings

[reaction: see text] Treatment of alkynyl allenes with [Rh(CO)(2)Cl](2) results in a formal [2 + 2 + 1] cycloaddition reaction. This reaction occurs with complete regioselectivity for a variety of substrates affording only 4-alkylidene cyclopentenones in good yields. Moreover, seven-membered rings have been prepared in high yields.     

Novel synthesis of highly functionalized pyrazolone systems via rearrangement of 5-phenyl-1-oxa-5,6-diazaspiro[2.4]heptane-4,7-diones

Epoxidation of 4-alkylidene(arylidene)-1-phenyl-3,5-pyrazolidinediones using alkaline hydrogen peroxide gave the corresponding 5-phenyl-1-oxa-5,6-diazaspiro[2.4]heptane-4,7-dione derivatives. Their reaction with nucleophilic reagents was investigated. The resulting products depend on the type of the diazaspiro compound and/or the nucleophile used.     

Allenes and transition metals: a diverging approach to heterocycles

[reaction: see text] An alkynyl allene has been converted to heterocycles possessing an alpha-alkylidene cyclopentenone, a 4-alkylidene cyclopentenone, or a cross-conjugated triene. Thus, a common intermediate has been converted to three structurally unique compounds by changing only the reaction conditions and, therefore, controlling various reaction pathways.     

Electrooxidative [3 + 2] annulation of amidines with alkenes for the synthesis of spiroimidazolines

The electrooxidative [3 + 2] annulation of amidines with 2-arylideneindane-1,3-diones or 4-alkylidene pyrazolones is reported using NaI as a redox catalyst and electrolyte under constant current electrolysis in an undivided cell. The current strategy features excellent functional group tolerance, simple operation, and mild conditions, thus providing an environmentally benign and efficient access to spiroimidazolines in moderate to good yields.     

HIGHLY STEREOSELECTIVE SYNTHESIS OF DIALKYL 2-ALKYLIDENE GLUTARATES

Nucleophelic substitution of dialkyl (E)-2-bromomethylene glutarates 2 by magnesium dialkyl cuprates generated in situ provided a regio and highly stereoselective methodology for the synthesis of dialkyl 2-alkylidene glutarates 3 in good yields.