Diastereoselective alkylations of oxazolidinone glycolates: a useful extension of the Evans asymmetric alkylation

[reaction: see text] The diastereoselective alkylation of glycolate oxazolidinones has been demonstrated as a method for the enantioselective preparation of alpha-alkoxy carboxylic acid derivatives and selectively protected 1,2-diols. Various protecting groups on the glycolate hydroxyl and multiple substitution patterns on allylic iodides are tolerated in the alkylation. Yields for the alkylations are typically 70-85% with diastereoselectivities of >98:2.     

Synthesis of (R)-2-(benzyloxy)-tetrahydro-5,5-dimethylfuran by a new oxidative rearrangement

The rearrangement under oxidative conditions of 3-(benzyloxy)-tetrahydro- 2,6,6-trimethyl-2H-pyran-2-carbaldehydes to afford a chiral protected tetrahydrofuran lactol is described.     

Synthesis of functionalized polycyclic compounds via a novel aromatic oxy-Cope rearrangement

Polycyclic compounds have been prepared by aromatic dianionic oxy-Cope rearrangements involving the π bonds of two phenyl rings in a [3,3] sigmatropic rearrangement.     

Synthesis of the first water-soluble C2-symmetric bis(oxazolidinone) as a potential bifunctional chiral auxiliary

The first water-soluble C₂-symmetric bis(oxazolidinone) 1, a potential bifunctional chiral auxiliary, has been synthesized via regioselective intramolecular cyclization of a biscarbamate. The sodium enolate derived from N,N′-di(phenylacetyl)bis(oxazolidinone) 7 reacts with methyl iodide with high facial selectivity (95:5).     

Synthesis of 9-alkylidene-9H-fluorenes by a novel palladium-catalyzed rearrangement

In the presence of a palladium catalyst and NaOAc, aryl iodides react with 1-aryl-1-alkynes to afford 9-alkylidene-9H-fluorenes in good yields. This process appears to involve (1) oxidative addition of the aryl iodide to Pd(0), (2) alkyne insertion, (3) rearrangement of the resulting vinylic palladium intermediate to an arylpalladium species, and (4) aryl-aryl coupling with simultaneous regeneration of the Pd(0) catalyst.     

Design and synthesis of a new polymer-supported Evans-type oxazolidinone: an efficient chiral auxiliary in the solid-phase asymmetric alkylation reactions

Wang resin-supported Evans' chiral auxiliary (23) was designed based on a novel polymer-anchoring strategy, which utilizes the 5-position of the oxazolidinone ring, and its new synthetic route applicable to multi-gram preparation in just a day was developed. Solid-phase Evans' asymmetric alkylation on 23-derived N-acylimide resin and following lithium hydroperoxide-mediated chemoselective hydrolysis afforded the corresponding α-branched carboxylic acids in desired high stereoselectivities (up to 97% ee) and moderate to good overall yield (up to 70%, for 3 steps), which were comparable to those of the conventional solution-phase methods. Furthermore, recovery and recycling of the polymer-supported chiral auxiliary were successfully achieved without decreasing the stereoselectivity of the product. Therefore, this is the first successful example that the solid-phase Evans' asymmetric enolate-alkylation was efficiently performed on the solid-support, and it is concluded that the connection to the solid-support via the 5-position of the oxazolidinone ring is an ideal strategy in the solid-phase Evans' chiral auxiliary.     

A novel rearrangement of alkyl (n-alkylamido) methyl sulfides

The finding of a new rearrangement of alkyl (N-alkylamido) methyl sulfides promoted by strong bases such as NaH, LDA, and t-BuLi is described. The reaction induces a migration of the alkyl group linked to the sulfur to the amide carbonyl giving the corresponding ketone.     

A novel rearrangement of 2(5H)-furanones

A novel rearrangement of 2(5H)-furanones is described. When refluxed in aq. Ethanolic solution in the presence of excess KOH, the 2,5-dihydro-2-oxofuran-3-carboxamides 6 underwent a novel rearrangement to the corresponding 4,5-dihydro-4-oxo-2-(phenylamino)-3-furancarboxylic acids 1 in moderate-to-excellent yields.     

Synthesis of orthogonally protected (R)- and (S)-2-methylcysteine via an enzymatic desymmeterization and Curtius rearrangement

A synthesis of differentially protected (R)- and (S)-2-methylcysteines is described. Monomethylation of dimethylmalonate followed by alkylation with tert-butylchloromethyl sulfide gave an achiral diester. Desymmeterization by selective hydrolysis of one ester with pig-liver esterase gave the acid in 97% chemical yield and 91% enantiomeric excess. Heating this acid with diphenylphosphoryl azide followed by 4-methoxybenzyl alcohol gave protected (R)-2-methylcysteine. Alternately, the acid and ester groups were interchanged and heated with diphenylphosphoryl azide followed by 4-methoxybenzyl alcohol, giving protected (S)-2-methylcysteine.     

On the mechanism of a novel 3(2H)-Furanone-2(5H)-furanone rearrangement

The isolation of a stable intermediate product and the mechanism of a novel 3(2H)-furanone-2(5H)-furanone rearrangement that led to the facile preparation of a new class of γ-lactone amides 2 and 4 are discussed.     

Enantioselective synthesis of (R)- and (S)-alpha-alkylcysteines via phase-transfer catalytic alkylation

We reported efficient enantioselective synthetic methodologies for (R)-alpha-alkylcysteines and (S)-alpha-alkylcysteines. The phase-transfer catalytic alkylation of 2-phenyl-2-thiazoline-4-carboxylic acid tert-butyl ester and 2-o-biphenyl-2-thiazoline-4-carboxylic acid tert-butyl ester, in the presence of chiral catalysts (1 or 2), gave the corresponding alkylated products, which could be hydrolyzed to provide (R)-alpha-alkylcysteines (67->99% ee) and (S)-alpha-alkylcysteines (66-88% ee), respectively.     

Synthesis of tetramethyldisilane-bridged bis(1-indenyl) tetracarbonyl di-iron: A novel thermal rearrangement reaction between the Si-Si and Fe-Fe bonds

The title complex (Me₂SiSiMe₂)(η⁵-l-indenyl)Fe(CO)]₂(μ-CO)₂ (1) was prepared by the reaction of 1,2-bis(1-indenyl)tetramethyl-disilane and Fe(CO)₅ in refluxing heptane. Its thermal rearrangement product [Me₂Si(η⁵-1-indenyl)Fe(CO)₂]₂ (2) was also obtained from the reaction. 1 in refluxing xylene can be readily converted into 2. The crystal structures of the cis isomer 1c and the trans isomer 2t were determined by X-ray diffraction.     

Macromolecular-chain rearrangement during synthesis of poly(N-phenylurethanes)

Poly(N-phenyliminocarbonates) capable of converting into poly(N-phenylurethanes) via thermal treatment at 300°C for 9 h through the Chapman mechanism were prepared via the polycondensation of bisphenols with plenyliminophosgene. The resulting polymers are soluble in chlorinated hydrocarbons and amide solvents. The polymers are characteristic by glass-transition and 10%-weight-loss temperatures during heating in air of 165–210 and 455–490°C, respectively.     

Synthesis of 1-arylmethyl-2-(2-cyanoethyl)aziridines and their rearrangement into novel 2-(aminomethyl)cyclopropanecarbonitriles

1-Arylmethyl-2-(bromomethyl)aziridines were transformed into novel 2-(2-cyanoethyl)aziridines upon treatment with alpha-lithiated trimethylsilylacetonitrile in THF in an efficient and straightforward approach. The latter aziridines underwent ring opening by reaction with benzyl bromide in acetonitrile, affording 5-amino-4-bromopentanenitriles through a regiospecific ring opening of intermediate aziridinium salts by bromide. Further elaboration of these gamma-bromonitriles resulted in the synthesis of novel 2-[N,N-bis(arylmethyl)aminomethyl]cyclopropanecarbonitriles in high yields by means of a 1,3-cyclization protocol upon treatment with KOtBu in THF.     

Tandem molecular rearrangement in the alkylation of phenol with camphene

The alkylation of phenol with camphene in the presence of boron trifluoride in glacial acetic acid was accompanied by tandem molecular rearrangement with formation of a mixture of ortho- and para-substituted phenols having 1,7,7-trimethylbicyclo[2.2.1]hept-exo-2-yl and 5,5,6-trimethylbicyclo[2.2.1]hept-exo-2-yl substituents. The same products were obtained by rearrangement of 1,7,7-trimethylbicyclo[2.2.1]hept-exo-2-yloxybenzene under analogous conditions. Similar reactions performed in the presence of aluminum phenoxide as catalyst resulted in predominant formation of the corresponding ortho-substituted phenols.     

A novel rearrangement of 1-(2-aminoaryl)imidazoles

6-Ethyl-2,4-bis(1H-imidazol-1-yl)pyrimidin-5-amine was found to undergo a novel rearrangement in the presence of acetic anhydride. The structure of the rearrangement product was deduced using a combination of one- and two-dimensional nmr methods. Confirmation of the structure was obtained by unambiguous synthesis of a reduced analog and establishment of the identity of this material with material prepared by reduction of the rearrangement product. Examination of three related cases indicated that the rearrangement process is significant only when both positions adjacent to the aryl amino group are substituted.     

Synthesis and absolute configuration of novel N,O-psiconucleosides using (R)-N-phenylpantolactam as a resolution agent

A series of novel N,O-psiconucleosides has been prepared in both enantiomeric forms by resolution of an advanced racemic synthetic intermediate using (R)-N-phenylpantolactam as a chiral resolution agent. The absolute configuration of all of these compounds has been unequivocally established by chemical correlation with the novel (R)- or (S)-1-methyl-5-phenylpyrrolidine-2,3-dione, prepared from the known (R)- and (S)-1-methyl-5-phenylpyrrolidin-2-one, respectively.     

Synthesis of (24R)-homobrassinolide

The synthesis from stigmasterol of C-29 brassinosteroids containing an (R)-ethyl group at C24 — (24R)-homocastasterone and (24R)-homobrassinolide — is described. The structure of the carbon skeleton of the side-chain was achieved by condensing a C-22 aldehyde with the appropriate sulfone