Convenient synthesis of optically active α‐hydroxyphosphinic acids

The reaction of O‐menthyl phenylphosphonite 1 with aromatic aldehydes in the presence of Me₃SiCl provided the O‐menthyl α‐hydroxyphosphinates 2 . Acidic hydrolysis of 2 gave the corresponding α‐hydroxyphosphinic acids 3 . The (+)‐enantiomer of 3a and 3b , adduct of benzaldehyde and 4‐methylbenzaldehyde respectively, were obtained via multiple recrystallization. The absolute configuration of (+)‐ 3a was determined as S by X‐ray crystallography. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:312–315, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10150     

Synthesis of optically active 6-substituted 2-(aminomethyl)chromans

Three novel, optically active, 6-substituted 2-(aminomethyl)chromans were synthesized from readily available chroman 2-carboxylic acid precursors. These chroman-containing primary amines are useful building blocks for the synthesis of chroman-derived pharmaceutical agents.     

Polymerization of optically active β-substituted β-propiolactones. IV. β-1,1-dichloroalkyl β-propiolactones polymerized with aluminum triisopropoxide

The polymerization of three optically active β-1,1-dichloroalkyl β-propiolactones has been investigated in toluene, at 55°C, using aluminum triisopropoxide (Al(OiPr)₃) as initiator in a range of monomer/initiator molar ratios smaller than 150. β-1,1-dichloroethyl β-propiolactone polymerizes according to a living mechanism. However, the ability to polymerize decreases with an increase in the length of the alkyl substituent. For instance, β-1,1-dichloro-n-propyl β-propiolactone is obtained only in low yields, whereas β-1,1-dichloro-n-butyl β-propiolactone does not polymerize at all. Actually, each of the lactones investigated reacts with Al(OiPr)₃ in an initiation step that obeys a coordination-insertion mechanism. However, the size of the chloroalkyl substituent has a critical effect on the propagation: when the alkyl group contains more than two methylene units, the insertion of a second monomer becomes exceedingly slow.     

A new synthesis of α-substituted δ-carbolines

The paper describes a new general synthesis of α-substituted δ-carbolines based on key steps such as metalation, cross-coupling and cyclization.     

Asymmetric synthesis of protected α-fluoroglycines

Single crystal x-ray structure determination of a key fluoroiodoacetamide gives access to protected α-fluoroglycines of known absolute stereochemistry.     

Polymerization and properties of optically active α-(p-substituted benzenesulfonamido)-β-lactones

Optically active α-(p-substituted benzenesulfonamido)-β-lactones having as para substituents OMe, Me, H, and Cl were polymerized in bulk, in ethyl acetate solution with triethylamine or betaine, and in dioxane with butyllithium as initiators. The rate of polymerization was followed by the change of specific rotation with time and was decreasing in following order of para substituents: OMe > Me > H > Cl. The relative reactivity in logarithmic form was plotted against Hammett's σ functions showing a linear relationship with reaction constant ρ = ?0.57.     

Preparation,characterization, and porperties of optically active poly(α-methyl-α-ethyl-β-propiolactones)

S(?) and R(+) enantiomers of α-methyl-α-ethyl-β-propiolactone (MEEPL) were prepared in an eight-step synthesis with respective optical purities of 99 and 97% determined by ¹H-NMR (250 MHz) spectroscopy. Polymers (PMEPL) of different enatiomeric compositions were prepared with an anionic-type initiator. Substantial differences in physical properties were observed between the racemic and optically pure polymers; for example, the melting point of the latter is 42°C higher than that of the former. Chiroptical properties of PMEPLs are reported. The ¹³C-NMR (100.62 MHz) spectra of the polymers indicated that the distribution of configurational units in the macromolecular chain is random.     

Asymmetric hydrogenation of enol phosphinates catalyzed by a chiral ferrocenylphosphine-rhodium complex. Asymmetric synthesis of optically active secondary alkyl alcohols

Catalytic asymmetric synthesis of secondary alkyl alcohols (up to 78% ee) was accomplished by asymmetric hydrogenation of enol diphenylphosphinates, derived from prochiral ketones such as acetophenone, 3-methyl-2-butanone, and 2-octanone, in the presence of a cationic rhodium complex of (R)-1-[(C)-1′,2-bis(diphenylphosphino)ferrocenyl]ethanol (BPPFOH).     

Synthesis and polymerization of racemic and optically active β-substituted β-propiolactones. III. β-monosubstituted monomers and polymers

Optically active β-(1,1-dichloroethyl)-β-propiolactone (CH₃CCl₂-PL), β-(1,1-dichloropropyl)-β-propiolactone (C₂H₅CCl₂-PL), and β-(1,1-dichlorobutyl)-β-propiolactone (C₃H₇CCl₂-PL) were synthesized with enantiomeric excesses of 100, 100, and 84%, respectively. Polymerization was conducted in bulk and toluene solution, under vacuum, using mainly ZnEt₂/H₂O as initiator. Osmometry analyses indicate molecular weights in the range 10,000–25,000. The polymers thus prepared are semi-crystalline and show large optical rotation values.¹³ C-NMR was used to show that they have a high degree of isotacticity, indicating that little or no racemization occurs in the course of polymerization. Glass transition, melting and decomposition temperatures are given as a function of the size of the substituent, and their variations are discussed.     

Synthesis and characterization of α,α'-bis(aminomethyl)oligothiophenes and their related compounds

We have synthesized and characterized a series of novel compounds of α,α'-bis(arninomethyl)oligothiophenes and their related compounds whose degree of polymerization spans two (dimer) to five (pentamer). The compounds presented in our studies are α,α'-bis[(2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopenthyl)methyl]oligothiophene, α,α'-bis(aminomethyl)oligothiophene dihydrochloride and α,α'-bis(aminomethyl)oligothiophene. These compounds exhibit desired chemical activity while maintaining controllable electronic properties. The synthetic processes of the oligothiophenes are as follows: 2-aminomethylthiophene is first ‘protected’ and the thiophene rings are coupled using standard Grignard methods. The protected groups are removed at the final stage of the reaction. The compounds show unique properties; for example α,α'-bis(aminomethyl)oligothiophene dihydrochloride is soluble in water. The results of electronic spectra and titration are also presented.     

Synthesis of optically active N‐protected α‐aminoketones and α‐amino alcohols

A series of optically active N‐protected α‐aminoketones were synthesized via the Grignard reaction of the Weinreb amides of the N‐tert‐butoxycarbonyl amino acids. Reduction of the α‐aminoketones by sodium borohydride resulted in the corresponding 1,2‐amino alcohols. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:603–606, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10195     

Amine-induced rearrangements of 2-bromo-1-(1H-indol-3-yl)-2-methyl-1-propanones: A new route to α-substituted indole-3-acetamides, β-substituted tryptamines, α-substituted indole-3-acetic acids and indole β-aminoketones

The reaction of 2-bromo-1-(1H-indol-3-yl)-2-methyl-1-propanone ( 1 ) and 2-bromo-1-(1-methyl-1H-indol-3-yl)-2-methyl-1-propanone ( 2 ) with primary amines proceeds in good yields to produce rearranged amides by a proposed pseudo-Favorskii mechanism. These amides in turn can either be reduced to produce β-substituted tryptamines or hydrolyzed to produce substituted indole-3-acetic acids. When the reaction is carried out using bulky primary or secondary amines, β-aminoketones are produced by elimination of hydrogen bromide followed by Michael addition. When hindered secondary amines or tertiary amines are used, elimination to the α,β-unsaturated ketones occurs.     

Synthesis of new optically active α,α′,β‐trisubstituted‐β‐lactones as monomers for stereoregular biopolyesters

Various optically active (4R)‐alkyloxycarbonyl‐3,3‐dialkyl‐2‐oxetanones as monomers were synthesized from L‐(S)‐malic acid in six steps to prepare a new family of stereopolyesters for biomedical applications. The synthesis began with an esterification followed of a dialkylation in the aim to introduce hydrophobic groups as methyl or reactive group as allyl. Then, a saponification has permitted to obtain the corresponding diacids that reacted with appropriate alcohols to furnish different monoesters. The last and most important step was activation of hydroxyl group of monoesters with the asymmetric carbon configuration inversion according to the Mitsunobu reaction. Thus, this reaction has provided lactones from monoesters with 100% enantiomeric excess which was confirmed by ¹H NMR and by the synthesis of corresponding isotactic and semicrystalline homopolyesters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2586–2597     

Studies on furan derivatives IV. A simple preparation of α-substituted β-(5-nitro-2-furyl)ethynyls from α-substituted β-(5-nitro-2-furyl)vinylamines

α-Substituted β-(5-nitro-2-furyl)ethynyls were conveniently prepared by the deamination of α-substituted β-(5-nitro-2-furyl)vinylamines. Also the application of this reaction toward α,β-bis(p-nitrophenyl)vinylamine was examined and afforded α,β-bis(p-nitrophenyl)ethynyl as the main product.     

Polymerization of α,α-disubstituted β-propiolactones and lactams. VII. Stereoregular polymers from optically active lactones

Optically active α-phenyl-ααethyl-β-propiolactone of high optical purity was prepared and polymerized by homogeneous anionic initiation to the isotactic polyester. The racemic and isotactic polymers had apparently different crystalline properties suggesting that the former may be syndiotactic or may crystallize with unit cells containing both R and S blocks. Similar attempts to prepare α-methyl-α-isopropyl-β-propiolactone of high optical purity were unsuccessful although a partially crystalline polymer was obtained from the racemic monomer.     

Asymmetric Dihydroxylations of β-Substituted N-(α,β-Enoyl)bornane-10,2-sultams

Pure (E)- or (Z)-enoylsultams 2 were Oxidized with OsO₄/N-Methylmorpholine N-oxide in a stereospecific and highly π-face-selective manner. Acetalization of the resulting 1,2-diols furnished, after purification, the stable, crystalline acetals 6 in >99% d.e. and in 63–74% overall yield from 2 . Reductive or hydrolytic cleavage of 6 gave enantiomerically pure alcohols 8 or carboxylic acids 9 with recovery of the sultan auxiliary 1 .     

A novel type of optically active helical polymers: Synthesis and characterization of poly(α,β‐unsaturated ketone)

New α,β‐unsaturated ketone monomers, menthyl vinyl ketone (MVK), and 1‐menthylbut‐3‐en‐2‐one (MBEK) were synthesized. The monomers were polymerized using butyllithium as an initiator. The polymer derived from MVK (poly‐MVK) had a tremendous specific optical rotation [α], which was as 32 times large as that of its monomer MVK. Poly‐MVK was confirmed to keep a prevailing helicity of backbone in solution by means of comparing the specific optical rotation and the CD spectra with that of MVK and the model compound such as ethyl menthyl ketone (EMK) and n‐hexyl menthyl ketone (n‐HMK). This conclusion was also confirmed by the fact that the specific optical rotation and the CD signal intensity of poly‐MBEK were not enough large due to backbone flexibility caused by the effective isolation of the main chain from the bulky menthyl. The excess value of one‐handed helicity of poly‐MVK decreased with the increase of polymerization temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1441–1448, 2010