Silicon-induced diastereoselectivity of the catalyzed phosphorylation of 1-(perfluoroalkyl)-ω (trialkylsilyl)alkan-1-ols

The stereochemistry of catalytic phosphorylation of 1-(perfluoroalkyl)--(trialkylsilyl)alkan-1-ols with pentavalent phosphorus acid monochlorides (phosphonochloridates, methyl(phenyl)phosphinic chloride, and phosphorochloridates) was studied. The effects of the structures of alcohols and phosphorylating agents on the degree of the reaction diastereoselectivity were investigated. Methylphosphonochloridates were found to react most stereoselectively; the diastereoselectivity of the phosphorylation is independent of the donor or acceptor character of substituents at the phosphorus atom, being determined by their volumes. In the series of silylalkanols, the diastereoselectivity of the reaction the higher the closer the Si atom to the reactive site of the molecule, the larger the volume of the perfluoroalkyl substituent, and the more pronounced the electron-withdrawing properties of the substituents at the Si atom. A reaction mechanism is proposed that rationalizes the stereoselectivity of the reaction.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1930–1936, September, 2004.     

Synthesis of 8-(ω-Chloroalkyl)-dipyrrinones

Dipyrrinones,typically brightyellow compounds with a long axis- polarizedπ- π* excita-tion in the1 4 π- electron- conjugated chromophore,such as xanthobilirubic acid methyl ester(XBRMe) ,are useful building blocks for the syntheses of biologically important tetrapyrrolepigments such as bilirubin(the yellow pigmentof jaundice) [1 ],and they have been extensivelyused as model dipyrrole pigments for the spectroscopic and the photochemical studies of linertetrapyrroles such as bilirubin and bil…     

Synthesis and photophysical properties of α,ω-bis(terpyridine)oligothiophenes

Four novel fully π-conjugated α,ω-bis(terpyridine)oligothiophenes characterized by NMR, IR, and HR-mass spectroscopy are presented and their electronic absorption/emission and redox properties are described based on both experiments and theoretical calculations. These compounds can be potentially utilized as building blocks for preparation of conjugated metallo-supramolecular polymers or dynamers and related functional materials.     

Synthesis and characterization of α,ω-dichloro-polymethylphenylsilane

The synthesis of a functional polysilane, α,ω-dichloro-polymethylphenylsilane (α,ω-dichloro-PMPS), based on the Wurtz-type reductive coupling, has been considered. A study of some reaction parameters shows that both yield and molecular weight distribution of α,ω-dichloro-PMPS can be greatly influenced by the work-up conditions, reaction time, monomer concentration and temperature during the initiation of the polymerization. By varying the synthesis conditions, different ratios of high and low molecular weight fractions were obtained. Samples of different molecular weight were isolated by fractional precipitation of the crude polymers. The chlorine-end functionalization was confirmed by ²⁹Si NMR spectroscopy and the concentration of end-groups was quantitatively determined by elemental analysis of chlorine.     

A New Synthesis of 1-(ω-Haloalkyl)-Imidazoles

Inconnechonwith0urreeenteffortStowardsthesynthesis0fartificialreceptorsandenzymescontalninginddazoles",itwasnecessarytoprepareaclassofl-(orhaloalkyl)-inddazolesassyntheticpreeursors.The0nlyreportinliteratureislindtedforthepreparationofl-(2-bromoethyl)inddazolebyreactingimidazolefirstwithethylenecarbonate,thenwiththionylbr0nddet0givea24.5%yield'.Therearenogeneralpreparativemethodsforthesecompounds.RecenUy,HorvathreportedasimPlemethodf0rthepreparationofl-substitutedinddazolesfromaHoffmann-type…     

Synthesis and mass spectrometric study of α,ω-bis(heptamethylcyclotetrasiloxanyloxy)oligodimethylsilanes

α,ω-Bis(heptamethylcyclotetrasiloxanyloxy)oligodimethylsilanes were synthesized by the reaction of dichlorodimethylsilane and 1,3-dichlorohexamethyltrisilane with hydroxyheptamethylcyclotetrasiloxane. The peculiarities of fragmentation of the compounds obtained by electron impact mass spectrometry are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1729–1733, September, 1999.     

Synthesis of optically active α-(allenyl)- and α-substituted-α-(allenyl)glycines

The synthesis of various types of optically active α-(allenylsilane-containing)glycines via a chirality-transferring ester-enolate Claisen rearrangement of α-acyloxy-α-alkynylsilanes is described. The conversion of the rearranged products into the optically active silicon-free α-(allenyl)- and α-substituted-α-(allenyl)glycines was achieved by the removal of the Me₂PhSi- or TMS group from the allene terminus.     

Synthesis and properties of α, α′ -bis -(p-benzylphenyl)xylene

Summary ,-bis-(p-Benzylphenyl)xylene was synthesized for the first time and its UV and infrared spectra determined.     

Synthesis of α-hydroxy(polyprenyl) bisphosphonates

Bisphosphonates derived from natural terpenes were synthesized by phosphonylation of corresponding aldehydes. The general strategy of introduction of the phosphonate groups into the polyprenol molecule involves successive treatment of a hydroxyl compound by Swern reagent to oxidize the C-OH group into C=O and a (EtO)₃P/[PyH]⁺ClO _? ⁴ mixture to phosphylate the resulting carbonyl compound.     

Synthesis and characterization of α-N,N-dihydroxyethylaminopropyl-ω-butylpolydimethylsiloxanes

A series of α-N,N-dihydroxyethylaminopropyl-ω-butylpolydimethylsiloxanes with different molecular weight were synthesized. The preparation included five steps which were hydroxyl protection, alkylation, anionic ring-opening polymerization, hydrosilylation and deprotection. The structure of reaction products was characterized by FT-IR, GC, 1H NMR. 2007 Qing Si Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.     

Synthesis and Reactivity of α-Bromo-4-(difluoromethylthio)acetophenone

A synthesis is reported for -bromo-4-difluoromethylthioacetophenone and the conditions for the condensation of this compound with 2-aminothiazole, 2-amino-5-chloropyridine, 2-amino-4,5-dihydro-3H-pyrrole, benzimidazoline-2-thione, oxadiazoline-2-thione, and thiourea were studied. S- and N-substituted azaheterocycles containing the 4-(difluoromethylthio)phenyl fragment were synthesized and characterized.     

Synthesis of new derivatives of α-mangostin (microreview)

Chemistry of Heterocyclic Compounds - This microreview presents the current state of research on functionalization of α-mangostin, a natural hydroxyxanthone. Examples of transformations are...     

Synthesis of N-substituted tetrapropargylamines by catalytic aminomethylation of α,ω-diacetylenes

Chemistry of Heterocyclic Compounds - A catalytic method was developed for the synthesis of N-substituted tetrapropargylamines by reactions of α,ω-diacetylenes with 1,5,3-dioxazepanes,...     

Synthesis of α-ω-Diamino Acids: An Efficient Preparation of DL-Homolysine and Protected Derivatives

Prior literature contains ample low-yield, multi-step precedents for the preparation of DL-homolysine (2,7-diaminoheptanoic acid). In a modified Albertson and Archer acetamidomalonic ester synthesis,¹ diethyl acetamidomalonate was alkylated, in the presence of sodium ethoxide, with 5-benzamido-1-chloropentane,² itself prepared from N-benzoylpiperidine and PCl₅ as described by Harris and Work,³ or from dihydropyran via 5-hydroxyvaleraldehyde⁴ as described by Wada.⁵ These multi-step methods have limited synthetic utility, due to low yields of electrophile preparation and of carbon-carbon bond formation, leading to an overall 10% yield of DL-homolysine. Takagi and Hayashi⁶ explored several approaches to D,L-homolysine. One of these involved a modification of the malonic ester synthesis where ethyl 5-bromocaporate was prepared from cyclohexanone⁷ and used to alkylate diethyl malonate, giving DL-homolysine, after two steps, in 1396 overall yield. In a second approach, Takagi and Hayashi performed end group transformations on a C-8 backbone, suberic acid, using a Schmidt reaction to prepare DL-homolysine, in 1196 yield after eight steps. More recently Kirret⁸ improved this method, through the use of a Hunsdiecker reaction, reducing the number of steps to six, giving DL-homolysine in 18% yield. These methods failed to meet our synthetic objectives of greater than 50% yield in a minimum number steps.     

Multigram Synthesis of α- and γ-((Hetera)cyclo)alkylpyridines through α-Arylation of (Hetero)aliphatic Nitriles

A systematic study on the S_nAr reaction of halogenated fluoropyridines and (hetero)aliphatic nitrile anions as an approach to the synthesis of functionalized pyridines bearing a (cyclo)alkyl or saturated heterocyclic substituent by is described. The scope of the method was demonstrated on a wide range of (hetero)aliphatic nitriles (including three- to six-membered cycloalkane derivatives and N-, O-, S-containing saturated heterocycles) and all isomeric halogenated 2-and 4-fluoropyridines. High chemo- and regioselectivity (i. e., exclusive substitution of the fluorine atom), as well as excellent scalability of the proposed reaction sequence were demonstrated (up to 450 g for the arylation step or up to 77 g of cycloalkylpyridine over two steps in a single run). The utility of the synthesized products was illustrated in the additional functional group transformations resulting in synthetically valuable pyridine-containing building blocks.     

Synthesis and characterization of α-{3-[2-hydroxy-3-(N-methyl-N-hydroxy-ethylamino)propoxy]propyl}-ω-butylpolydimethylsiloxanes.

α-{3-[2-hydroxy-3-(N-methyl-N-hydroxyethylamino)propoxy]propyl}-ω-butylpolydimethylsiloxanes Ⅲ with various moleculax weights were prepared by epoxy addition of α-[3-(2,3-epoxy-propoxy)propyl]-ω-butylpolydimethylsiloxanes Ⅱ and Nmethylmonoethanolamine.At each step.the outcome compounds were characterized through FT-IR and NMR spectra,the results showed that each step was successfully carried out and objective products were achieved.     

Synthesis and structural study of α-amino- and α,ω-diamino oligoamides-11

α-Amino (MAO) and α,ω-diamino (DAO) oligoamides were prepared using dodecylamine or 1,6 diaminohexane as a chain limitator. These were characterized by GPC, ¹H-NMR and ¹³C-NMR; molecular models: N-dodecyldodecanamide and 1,6 bis dodecylaminohexane; trifluoroacetylation was used to dissolve the oligoamides. DAO prepared in the melt contains two types of chains, depending on the position of the limitator. When oligomers were prepared in solution using the Yamazaki method, the presence of residual phosphorus derivatives in the oligoamides could not be avoided.     

Concise Synthesis of α-(Hydroxymethyl) Alkyl and Aryl Vinyl Ketones

2,4-Diketoesters 2 have first been reported as starting materials for the synthesis of a new class of α-hydroxymethyl-α,β-unsaturated ketones 3. Thus, under heterogeneous liquid–liquid medium in the presence of concentrated aqueous potassium carbonate as a base, both aliphatic and aromatic 2,4-dioxoalkanoates 2 react with aqueous formaldehyde to afford the corresponding ketones 3 in fair to good yields.     

Synthesis of chiral α-(tetrazol-1-yl)-substituted carboxylic acids

Optically active α-(tetrazol-1-yl)-substituted carboxylic acid OBO-esters were synthesized from the corresponding a-isocyano OBO-esters and trimethylsilyl azide in up to 92% yield. Subsequent acidic hydrolysis proceeds without epimerization and makes it possible to prepare enantiomerically pure α-(tetrazol-1-yl)-substituted carboxylic acids in up to 89% yield.

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