Reaction de diels-alder intramoleculaire de 3h-pyrroles

The first intramolecular Diels-Alder reaction of 3-alkenyl 3H-pyrroles (2-azadiene system) is related. These 3H-pyrroles are $\text{in situ}$ generated from 2H-pyrroles.     

Reactivite des derives organomanganeux—VIII : Préparation de cétones par acylation d'organomanganeux. Influence de la nature de l'agent acylant,des solvants et des ligands

The influence of the nature of acylating reagents, solvents and ligands on the preparation of ketones by acylation of organomanganous reagents is studied. Thus acid chlorides in ether, symmetrical acid anhydrides in ether or THF and mixed carboxylic-carbonic anhydrides (R'COOCOOEt) in ether are compared, they lead to the corresponding ketones with good or excellent yields. Some problems of reproductibility are encountered and discussed when mixed anhydrides R'COOCOOEt are used in THF. The addition of a great variety of cosolvents (e.g. C₆H₆, AcOEt, CO₃Et₂, CH₂CN, CH₂CL₂, . .) to the reaction mixture before addition of the acylating reagent does not affect the yield of ketones. In comparison the complexation of organomanganous reagents by several ligands (e.g. Me₂S or Ph₃P) has no subsequent effect on their acylation. The main limitation for the choice of solvents or ligands is the use of amino derivatives which generally lead to a very low yield of ketones (e.g. C₅H₅N, TMEDA, Et₃N) or unreproducible yields (e.g. HMPA). Two applications of these studies are described:The stabilization of s or t-alkyl manganous derivatives by complexation which leads to the best yield of the corresponding ketonesThe use of a cosolvent in order to increase the yield when mixed anhydrides R'COOCOOEt are used in THF.     

Etude des petits cycles—XXX : Extension de cycle generale de cyclopropanols: Halomethyl-1, hydroxymethyl-1, vinyl-1, acyl-1, cyclopropanols,et des oxaspiropentanes en cyclobutanones

Cyclopropanols 5, 6 and 2 with substituent groups (-CH₂OH, -CH₂OTs, -CH₂Br) in the 1-position, and oxaspiropentane 8, have been prepared from methylenecyclopropane. Cyclopropanols with vinyl groups in the 1-position (1-vinyl 12, 1-cyclopentenyl 13 and 1-cyclohexenyl 14) and 1-cyclopropylcyclopropanol 20 have been prepared from 1, 3-dichloroacetone.Each of the compounds readily undergoes ring expansion to the corresponding cyclobutanones. The reaction provides a simple route to cyclobutanones, the parent ketone itself being easily obtained from oxaspiropentane 8.     

Selective crown ether based macrocyclization: a model case study from N,N-bis(2-hydroxyalkylbenzyl)alkylamine

A model case of selective crown ether based macrocycles, i.e., [1+1] or [2+2] macrocycles, obtained from a simple reaction of N,N-bis(2-hydroxyalkylbenzyl)alkylamine, HBA, and ditosylated compounds is proposed. For HBA with the methyl group at ortho and para positions, and at N atom, 1, the reaction between this derivative and the ditosylated compound with three, four, five, or eight atom chain length gives only a [1+1] macrocycle. For HBA with the methyl group at ortho and para positions, but a cyclohexyl group at N atom, 2, the reaction gives both [1+1] and [2+2] macrocyclic types when reacting with the ditosylated compound. The present work indicates that the structure of HBA induces selective macrocyclization to provide both [1+1] and [2+2] macrocycles.     

Synthese de cetones aliphatiques encombrees : Action des organolithiens sur les dimethyl-4,4 oxazolines-2. Addition des organometalliques sur les sels de dimethyl-4,4 oxazolinium-2

α,α-Disubstituted ketones result from the reaction of organolithium compounds with substituted 4,4-dimethyl-2-oxazolines, 4, after hydrolysis of the intermediate enamine. Alkylation of the latter also permits the synthesis of α,α,α-trisubstituted ketones. α,α-Disubstituted ketones have been prepared by addition of organometallic reagents to 4,4-dimethyl-2-oxazolinium salts, 6. The efficiency of this method has been compared to that of other currently used methods.     

New strategy to the synthesis of (N → B) phenyl[N-alkyliminodiacetate-O,O′,N]boranes: The crystal structure of (N → B) phenyl[N-benzyliminodiacetate-O,O′,N]borane, (N → B)phenyl[N-(4-methyl)benzyliminodiacetate-O,O′,N]borane and (N → B) phenyl[N-phenacyliminodiacetate-O,O′,N]borane

A new, mild and friendly method for the synthesis of (N → B) phenyl[N-alkyliminodiacetate-O,O′,N]boranes 2–7 is reported. All compounds were identified by ¹H, ¹¹B, ¹³C NMR and their high resolution mass spectra (HRMS) are reported. The structure of the compounds 2, 4 and 5 were established by single crystal X-ray. Compounds 2 and 4 crystallized with two independent molecules 2A, 2B and 4A, 4B, respectively in the asymmetric unit. These molecular structures established the bicyclic structure showing a N → B bond length of 1.666 (2) Å for 2A, 1.675 (2) Å for 2B, 1.675 (3) Å for 4A, 1.663 (3) Å for 4B and 1.679 (2) Å for 5, as well as different torsion angles of the junction, 28.70 (2)° (C11–B1–N6–C17) for 2A, 21.50 (2)° (C11a–B1a–N6a–C17a) for 2B, 25.76 (0.26)° (C11–B1–N6–C17) for 4A, 21.96 (0.28)° (C11a–B1a–N6a–C17a) for 4B and −29.22 (0.20)° (C5–N1–B1–C13) for 5.     

Reactions of N,N-diisopropyl-2-aminoethylp-fluorobenzene thiosulfonate with oxidising agents

The behaviour of N,N-diisopropyl-2-aminoethyl p-fluorobenzene thiosulfonate 3, which may be considered as a weakly toxic chemical analogue of VX agent, was investigated against oxidising agents. As VX 1, this compound exhibits the same tendency to give S–S bond cleavage. Its degradation by Curox® shows the formation of the N-oxide 6 which subsequently gives the sulfonate 7 by hydrolysis. The action of hydrogen peroxide, with or without boric acid, leads to the sulfinate 4 by S-S bond cleavage. Its oxidation gives sulfonate 7. Finally, reactions of MMPP and m-CPBA afford sulfonate 7 but no intermediates are highlighted with these reagents.     

Analyse conformationnelle de derives du thiophane,des sulfoxydes et sulfones correspondants

The conformations of biotin 1, cis 3,4-isopropylidenedioxythiophane 2, its 2,5-methylated homologs, 3, 4 and 5 and those of the corresponding sulfoxides and sulfones have been studied by NMR. Coupling constants, temperature and solvent effects show that all these compounds exist in a highly preferred conformation, the thiophane being in the envelope form with the sulphur atom out of the plane. In series 1, 2, 3 and 5 the arrangement is of the “boat-chair” type, in series 4 of the “crown” type, the sulphur being respectively cis and trans with respect to the other ring.     

Novel C2-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands: synthesis and application in asymmetric diethylzinc addition to aldehydes

First synthesis of C₂-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands is described. The Mukaiyama–Michael reaction was applied as an important reaction for the synthesis of 2,2-bipyridylpropane 9. Among the ligands synthesized, ligand 11 exhibits excellent chiral induction (up to 97% ee) in diethylzinc addition to various aldehydes. The use of additional Lewis acid such as Ti(OⁱPr)₄ in diethylzinc addition reaction is not required for the present catalytic system.     

Kondensationen mit hydrazin-N,N′-dicarbonsäure-diamidin—XVII : 4,5-dialkylderivate des 2,7-diamino-imidazo[5,1-f]-as-triazins

In interactions of β-dicarbonyl compounds (2) with azodicarboxamidine (1), the primary reaction step consists of the addition of the active methylene group in 2 to the NN double bond in 1. Via the addition product 3 thus formed, 2,7-diamino-4,5-dialkyl-imidazo[5,1-f]-as-triazines (4) are produced through condensation. 3,5-Heptanedione (2a), 4,6-nonanedione (2b), and 2,6-dimethyl-3,5- heptanedione (2c) have been used as β-dicarbonyl compounds.     

Preparation,isomerisation et configuration absolue des “hydrates” de thymidine

The (+) and (?) cis-6-hydroxy-5,6-dihydrothymidines 4a and 5a have been prepared by mild reduction of (+) and (?) trans-5-bromo-6-hydroxy-5,6-dihydrothymidine 2a and 3a. The trans “hydrates” 6a and 7a have been prepared by warming 4a or 5a in alkaline aqueous solution at 60°C. The isomerization of 4a, 5a, 6a and 7a involved the opening of the pyrimidine ring at 1,6 position and subsequent keto-enolisation. The characterization of the configurations of “hydrates” is based on the specific formation of the enantiomeric forms of 6-hydroxy-5,6-dihydrothymine by radiation-induced degradation of 4a, 5a, 6a, 7a and 5,6-dihydrothymine 5S8b.     

Rapid, microwave-assisted synthesis of N1-substituted 3-amino-1,2,4-triazoles

A robust, regioselective synthesis of 3-amino-1,2,4-triazoles is described. This reaction employs a key intermediate 2, which is coupled to carboxylic acids in good yields to afford intermediates 3a-d. These entities, in turn, react with a variety of hydrazines or hydrazine hydrochlorides to provide proposed intermediates 4a-j, which under microwave conditions cyclize to the desired 3-amino-1,2,4-triazoles (compounds 5a-j). This approach permits the rapid synthesis of regioselective N1-substituted 3-amino-1,2,4-triazoles, and is shown to afford a variety of such compounds in 34-70% isolated yields.     

Reactivity of intramolecularly coordinated aluminum compounds to R3EOH (E = Sn,Si). Remarkable migration of N,C,N and O,C,O pincer ligands

The reaction of organoaluminum compounds containing O,C,O or N,C,N chelating (so called pincer) ligands [2,6-(YCH₂)₂C₆H₃]AlⁱBu₂ (Y = MeO 1, ^tBuO 2, Me₂N 3) with R₃SnOH (R = Ph or Me) gives tetraorganotin complexes [2,6-(YCH₂)₂C₆H₃]SnR₃ (Y = MeO, R = Ph 4, Y = MeO, R = Me 5; Y = ^tBuO, R = Ph 6, Y = ^tBuO, R = Me 7; Y = Me₂N, R = Ph 8, Y = Me₂N, R = Me 9) as the result of migration of O,C,O or N,C,N pincer ligands from aluminum to tin atom. Reaction of 1 and 2 with (ⁿBu₃Sn)₂O proceeded in similar fashion resulting in 10 and 11 ([2,6-(YCH₂)₂C₆H₃]SnⁿBu₃, Y = MeO 10; Y = ^tBuO 11) in mixture with ⁿBu₃SnⁱBu. The reaction 1 and 3 with 2 equiv. of Ph₃SiOH followed another reaction path and ([2,6-(YCH₂)₂C₆H₃]Al(OSiPh₃)₂, Y = MeO 12, Me₂N 13) were observed as the products of alkane elimination. The organotin derivatives 4–11 were characterized by the help of elemental analysis, ESI-MS technique, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopy and in the case 6 and 8 by single crystal X-ray diffraction (XRD). Compounds 12 and 13 were identified using elemental analysis,¹H, ¹³C, ²⁹Si NMR and IR spectroscopy.     

Etude des petits cycles—XXVIII : Regression de cycle generale de cyclobutanols—I. Halohydrines-1,2, diols-1,2 et epoxydes correspondants

Methods for preparing 2-bromo and 2-tosyloxy cyclobutanols (1a and 1b) and 1,2-cyclobutanediols (6, 7, 8, 10 and 11), starting from 2-oxocyclobutanol 5 and 1,2-cyclobutanedione 9, have been studied. The cyclobutanols 1a and 1b undergo ring contraction in basic media while the 1,2-cyclobutanediols contract in acidic media or on heating. This ring contraction, reported previously for epoxycyclobutanes, affords cyclopropyl aldehydes or ketones in high yields.     

Dimerisation des polyphenyl-allenes—I : Chloropolyphenyl-allenes: mecanisme de la reaction “Rubrenique”

Dimerization of chloropolyphenylallenes 1a-c occurs via bisallyl diradicals 2a-c, the closure of which leads either to 1,2-dialkylidene cyclobutanes 8b,c, or to the dihydronaphthalenic compounds 3a-c which afford after elimination of HCl and cyclization the naphthocyclobutenes 5a-c. The latter, by opening and cyclization involving a further loss of HCl, are readily transformed in high yields into the naphthacenes 7a-c Some 1,2-dialkylidene cyclobutanes 8 can also lead to naphthacenes 7 through thermal opening to give diradicals 2, followed by cyclization. This multi-step process furnishes a general explanation for the so-called “rubrene” reaction (the common name of 5,6,11,12-tetraphenyl naphthacene), a route to naphthacenes starting from polyphenyl propargylic compounds which behave as aliene precursors.     

A common strategy for the synthesis of (+)-gabosine N, (+)-gabosine O,and some carbapyranoses using a Nozaki–Hiyama–Kishi reaction and RCM

Stereoselective synthesis of carbasugars (+)-gabosine N 1 and (+)-gabosine O 2, carba-α-l-rhamnose 17, and carba-6-deoxy-α-l-talose 18 by using a Nozaki–Hiyama–Kishi (NHK) reaction and ring-closing metathesis.     

The synthesis of methyl N,N′-diacetyl-α-d-kasugaminide

The synthesis of methyl N,N′-diacetyl-α-d-kasugaminide (24) has been described. 3 was converted through hydroboration-amination to ethyl 4-acetamido-2, 3, 4, 6-tetradeoxy-α, β-dl-glucopyranosides (ethyl N-acetyl-αβ-dl-tolyposaminide) (7 and 8). Bromination of 7 and 8 gave the 2-bromo compounds (17, 18 and 19). Displacement of Br of 17 with N₃ and subsequent hydrogenation and resolution furnished d-kasugaminide. Synthesis of ethyl α-dl-forosaminide has also been described.     

Synthesis and crystal structure of [N,N′-bis(2,3,5,6-tetrafluorophenyl)-ethane-1,2-diaminato(2-)]dipyridineplatinum(II)

The reaction of PtCl₂en (en = ethane-1,2-diamine) with TlO₂CC₆F₅ in boiling pyridine unexpectedly yielded a polyfluorophenyl-stabilized ethane-1,2-diaminatoplatinum(II) complex, Pt[N(p-HC₆F₄)CH₂]₂(py)₂, 1a, the structure of which has been established by X-ray crystallography.     

Ylide von Heterocyclen,IV. Sulfonium- und Pyridinium-Ylide des Cumarins und des 2-Chinolons

The title compounds3 can be prepared either from the iodonium-ylides1 or from the chlorocompounds4. On treatment with hydrochloric acid the thiophanium-ylides3 C undergo ring cleavage to the chlorobutylsulfides5, also formed from4 and thiophane. The dimethylsulfonium-ylide8 is derived from activatedDMSO and7 b. TheOrtoleva-King reaction is discussed as an alternative method for preparing pyridiniumylides.     

A theoretical study of the reaction of N(4 S) with nitrogen dioxide on the N2O2 potential energy surface

The reaction of N(⁴ S) radical with NO₂ molecule has been studied theoretically using density functional theory and ab initio quantum chemistry method. Both singlet and triplet electronic state [N₂O₂] potential energy surfaces (PESs) are calculated at the G3B3 level of theory. Also, the highly cost-expensive coupled-cluster theory including single and double excitations and perturbative inclusion of triple excitations CCSD(T)/cc-pVTZ single-point energy calculation is performed on the basis of the geometries obtained at the Becke??s three parameter Lee-Yang-Parr B3LYP/6-311++G(d, p) level. On the singlet PES of the title reaction, it is shown that the most feasible pathway should be as follows. The atomic radical N attacking the NO bond of the NO₂ molecule first to form the adduct 1 N(NO)O, followed by one of the NO bond broken to give intermediate 2 ONNO, and then to the major products P1 (2NO). On the triplet PES of the title reaction, it is shown that the most favorable pathway should be the atomic radical N attacking the N-atom of NO₂ firstly to form the adduct 7 NN(OO), followed by one of the NO bonds breaking to give intermediate 8 NNOO, and then leading to the major products P2 (O₂ + N₂). As efficient routes to the reduction of NO₂ to form N₂ and O₂ are sought, both kinetic and thermodynamic considerations support the viability of this channel. All the involved transition states for generation of (2NO), (³O + N₂O), and (O₂ + N₂) lie much lower than the reactants. Thus, the novel reaction N + NO₂ can proceed effectively even at low temperatures and it is expected to play a role in both combustion and interstellar processes. The other reaction pathways are less competitive due to thermodynamical or kinetic factors. On the basis of the analysis of the kinetics of all path-ways through which the reactions proceed, we expect that the competitive power of reaction pathways may vary with experimental conditions for the title reaction. The calculated reaction heats of formation are in good agreement with that obtained experimentally.