Bicyclic Oxazolidines Research Articles

Chemoselective and Enantioselective Fluorescent Recognition of Prolinol

A highly chemoselective and enantioselective fluorescent probe has been discovered for the recognition of prolinol among various primary and secondary amine-based amino alcohols. The mechanistic studies including 1D and 2D 1H/13C NMR and mass spectroscopic analyses and DFT calculations have shown that the aldehyde group of the probe can react with prolinol to generate a bicyclic oxazolidine unit which, through a possible intramolecular hydrogen bond interaction, will lead to highly selective fluorescence enhancement.

Stereoconvergent synthesis of N-Boc-(2R,3S)-3-hydroxy-2-phenylpiperidine

The stereoconvergent synthesis of N-Boc-(2R,3S)-3-hydroxy-2-phenylpiperidine from (R)-1-(2-((tert-butyldimethylsilyl)oxy)-1-phenylethyl)piperidin-2-one is described. The key steps involved are α-hydroxylation of quiral lactam with O2, stereoconvergent reduction of (R)- or (S)-3-(benzyloxy)-piperidin-2-one with Red-Al® which afforded in both cases the trans-bicyclic oxazolidine in high stereoselectivity after chromatographic purification and a stereospecific Grignard addition to chiral bicyclic oxazolidine.

Synthesis, characterization of two new bicyclic oxazolidines and investigation of their optoelectronic properties using density functional theory

This paper presents a facile synthetic route to synthesise two new bicyclic oxazolidine compounds 3,5-bis(4- chlorophenyl)-7a-methyldihydro-1H-[1,3]oxazolo[3,4-c][1,3] oxazole (1) and 3,5-bis(2-methoxyphenyl)-7a-methyldihydro- 1H-[1,3]oxazolo[3,4-c][1,3]oxazole (2). The condensation reaction between 2-amino-2-methylpropane-1, 3-diol (ampdH2) and choloro- and methoxy- substituted aromatic aldehyde yielded the heterocyclic bicyclic compounds (1) and (2), respectively. The compounds are characterised by FT-IR and 1HNMR spectroscopy and structures are conclusively determined by single crystal X-ray diffraction analysis. The ground state geometries are optimised by using density functional theory (DFT) at B3LYP/6-31G** level of theory to compare the geometric parameters (bond lengths, bond angles and torsion angles) with the X-ray crystallographic data. The computed geometric parameters are in good agreement with the experimental data. To shed light on the electronic and photophysical properties, DFT/B3LYP/6-31G** and time dependent DFT have been applied, respectively. Intra-molecular charge transfer has been observed in both the compounds. The absorption wavelengths are calculated with and without the solvent (acetone, acetonitrile, dimethylformamide, dimethyl sulfoxide and methanol) at TD-B3LYP/6-31G** level of theory.

New Regio- and Stereoselective Cascades via Unstabilized Azomethine Ylide Cycloadditions for the Synthesis of Highly Substituted Tropane and Indolizidine Frameworks.

Multisubstituted tropanes and indolizidines have been prepared with high regio- and stereoselectivity by the [3+2] cycloaddition of unstabilized azomethine ylides generated from readily prepared trimethylsilyl-substituted 1,2-dihydropyridines via protonation or alkylation followed by desilylation. Starting from 1,2-dihydropyridines bearing a ring trimethylsilyl substituent at the 6-position, an intermolecular alkylation/desilylation provides endocyclic unstabilized ylides that successfully undergo cycloaddition with a range of symmetrical and unsymmetrical alkyne and alkene dipolarophiles to afford densely substituted tropanes incorporating quaternary carbons in good yields and with high regio- and stereoselectivity. Additionally, an intramolecular alkylation/desilylation/cycloaddition sequence provides convenient and rapid entry to bridged tricyclic tropane skeletons, allowing for five contiguous carbon stereocenters to be set in a single experimental operation and under mild conditions. Starting from 1,2-dihydropyridines with trimethylsilylmethyl groups on nitrogen, protonation followed by desilylation generates exocyclic unstabilized ylides that undergo cycloaddition with unsymmetrical alkynes to give indolizidines with good regio- and stereoselectivity. N-Trimethylsilylmethyl-1,2-dihydropyridines can also be alkylated and subsequently desilylated to give endocyclic unstabilized ylides that undergo intermolecular cycloadditions with carbonyl compounds to give bicyclic oxazolidine products in good overall yields. Moreover, an intramolecular alkylation/desilylation/cycloaddition sequence with the N-trimethylsilylmethyl-1,2-dihydropyridines affords tricyclic indolizidines that incorporate quaternary carbons and up to five stereocenters with good to excellent regio- and diastereoselectivity.

Straightforward synthesis of novel enantiopure α-trifluoromethylated azetidine 2-carboxylic acid and homoserines.

The straightforward syntheses of enantiopure (2R)-2-trifluoromethyl-2-carboxyazetidine and (R)- and (S)-trifluoromethylhomoserines are reported. The key step is a Strecker-type reaction on a common chiral CF3-containing bicyclic oxazolidine intermediate obtained by a condensation reaction of (R)-phenylglycinol and ethyl-4,4,4-trifluoroacetoacetate (ETFAA).

Formation of Heterocyclic and Polycyclic Compounds from Amino Alcohols and Dialdehydes

Amino alcohols typically react with aldehydes to produce oxazolidines. It was hypothesized that the condensation of several commercially available amino alcohols with dialdehydes would produce a series of bicyclic oxazolidines containing two secondary amines. However, there were remarkable differences in the type of products formed depending on the structure of the dicarbonyl compounds and the reaction conditions. When linear aliphatic dialdehydes such as glyoxal were used, the expected bis‐oxazolidines were not produced; instead, polycyclic structures or oxazines were formed. However, when cyclic dialdehydes such as 1,3/1,4 cyclohexane dicarboxaldehyde were used, they resulted in products bearing the desired oxazolidine moieties.

ChemInform Abstract: Aziridine‐2‐carboxaldehyde Dimers Undergo Homo‐Ugi 4‐Component‐5‐center Reactions.

AbstractEnantiopure aziridine‐substituted bicyclic oxazolidines, so called α‐aziridine aldehydes, are applied as substrates in Ugi and Passerini reactions to give highly functionalized scaffolds as diastereomeric mixtures.

Does FreezePruf Topical Spray Increase Plant Resistance to Freezing Stress?

One method of plant freeze protection involves the application of compounds that promote freeze avoidance or tolerance. FreezePruf, a commercially available product recently marketed to improve both freeze avoidance and tolerance, contains polyethylene glycol, potassium silicate, glycerol, silicone polyether surfactant, and a bicyclic oxazolidine antidessicant. The goal of the present study was to evaluate the protection level provided by FreezePruf using laboratory-based methods involving plants and plant parts from species capable and incapable of low-temperature acclimation. FreezePruf did not lower the freezing temperature of pepper (Capsicum annuum) seedlings, celosia (Celosia argentea) seedlings, detached tomato (Solanum lycopersicum) leaves, or postharvest tomato fruit. Spray application of the putative cryoprotectant did not increase the freeze tolerance of bermudagrass (Cynodon dactylon) crowns or stolons. It is possible that a greater level of protection could be achieved with other species or different experimental protocols.

Stereoselective Multicomponent Assembly of Enantiopure Oxazolopiperidines and -azepines

A multicomponent reaction (MCR) based on a cyclohydrocarbonylation (CHC) driven by hydroformylation was set up toward the efficient diastereoselective preparation of oxazolopiperidines (4a-e) and -azepines (7a-d). The bicyclic oxazolidines were obtained from chiral N-alkenylamino alcohols via transient cyclic iminium intermediates that underwent an intramolecular cyclization from the appendant oxygen. On the basis of a series of different experimental conditions, the diastereocontrol observed during the formation of the oxazolidines is best explained by the stereoelectronic effect induced by an A(1,3)-strain in a common cyclic iminium intermediate (A). This new sequence is suitable for diversity oriented syntheses, allowing the preparation of enantiopure (S)- and (R)-coniceine in five steps from commercially available material.

Enhancement of chromium uptake in tanning using oxazolidine

Monocyclic and bicyclic oxazolidines were offered at three different junctures of chrome tanning process viz. prior to BCS offer, along with BCS and after basification. It was found that oxazolidine when offered after basification brought about better chromium uptake and reduction of chromium load in the wastewater. Offer of oxazolidine was also varied. Increase in offer of oxazolidine from 0.25% to 1% was found to enhance the chromium uptake and decrease the chromium load in wastewater. But the increase in uptake was not proportionate to the increase in oxazolidine offer more than 0.75%. Offer of 1% Zoldine ZA 78 (monocyclic oxazolidine) and Zoldine ZE (bicyclic oxazolidine) after basification brought about 63.4% and 73.1% enhancement in chrome content in leather compared to control where oxazolidine was not offered. The tone of the wetblue was found to be altered moderately. However this did not call for any process adjustments in wet-finishing. The oxazolidine treated leathers were found to be immensely fuller and tighter. It was found experimentally that offer of 1% of oxazolidine facilitated reduction in the offer of syntans administered for filling and grain tightening by around 46%. Oxazolidine could bring about significant reduction in cost of chemicals apart from resulting environmental benefits due to enhancement of chromium uptake during tanning.

ChemInform Abstract: Remote Chiral Induction in the Thio-Claisen Rearrangement of Bicyclic Thiolactams.

Abstract A remote steric effect in the bicyclic lactam oxazolidine ring has been shown to affect the stereochemical outcome in the thio-Claisen rearrangement taking place in the piperidone ring.

ChemInform Abstract: Palladium‐Catalyzed Cyclization of Unsaturated β‐Amino Alcohols: A New Access to Enantiopure Bicyclic Oxazolidines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Syntheses of Enantiopure Bicyclic Oxazolidines Using Pd(II) Catalysts

Bicyclic oxazolidines are important intermediates in synthetic chemistry serving, for example, as valuable building blocks for nitrogen-containing heterocycles that belong to a class of biologically active compounds. Building on previous studies of the diastereoselective synthesis of various β-amino alcohols, the authors report herein a new palladium(II)-catalyzed cyclization of chiral unsaturated β-amino alcohols to afford enantiopure bicyclic oxazolidines with total regio- and stereocontrol.

Palladium-Catalyzed Cyclization of Unsaturated β-Amino Alcohols: A New Access to Enantiopure Bicyclic Oxazolidines

Chiral unsaturated beta-amino alcohols possessing a dialkylamino function cyclize in the presence of Pd(II) catalysts and reoxidants to afford enantiopure bicyclic oxazolidines with total regio- and stereocontrol. The scope and limitations of this transformation have been studied.

Rhodium-catalyzed carbonylation of allylaminoalcohols: Catalytic synthesis of N-(2-hydroxy-alkyl)-gamma-lactams and bicyclic oxazolidines

Gamma-lactams and bicyclic oxazolidines are important structural frameworks in both synthetic organic chemistry and related pharmacological fields. These heterocycles can be prepared by the rhodium-catalyzed carbonylation of unsaturated amines. In this work, allylaminoalcohols, derived from the aminolysis of cyclohexene oxide, styrene oxide, ( R)-(+)-limonene oxide, and ethyl-3-phenyl-glicidate, were employed as substrates. These allylaminoalcohols were carbonylated by employing RhClCO(PPh 3) 2 as a precatalyst under varying CO/H 2 mixtures, and moderate to excellent yields were obtained, depending on the substrate used. The results indicated that an increase in the chelating ability of the substrate (–OH and –NHR moieties) decreased the conversion and selectivity of the ensuing reaction. Additionally, the selectivity could be optimized to favor either the γ-lactams or the oxazolidines by controlling the CO/H 2 ratio. A large excess of CO provided a lactam selectivity of up to 90%, while a H 2-rich gas mixture improved the selectivity for oxazolidines, resulting from hydroformylation/cyclization. Studies of the reaction temperature indicated that an undesirable substrate deallylation reaction occurs at higher temperature (>100 °C). Further, kinetic studies have indicated that the oxazolidines and γ-lactams were formed through parallel routes. Unfortunately, the mechanism for oxazolidines formation is not yet well understood. However, our results have led us to propose a catalytic cycle based on hydroformylation/acetalyzation pathways. The γ-lactams formation follows a carbonylation route, mediated by a rhodium–carbamoylic intermediate, as previously reported. To this end, we have been able to prepare and isolate the corresponding iridium complex, which could be confirmed by X-ray crystallographic analysis.

Stereoselective Cycloaddition on Carbohydrates for the Synthesis of New Bicyclic Oxazolidines Bearing a Quaternary Bridgehead.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Stereoselective Cycloaddition on Carbohydrates for the Synthesis of New Bicyclic Oxazolidines Bearing a Quaternary Bridgehead

A new carbohydrate nitrone intramolecular cycloaddition reaction is described for the enantioselective synthesis of bicyclic oxazolidines. By choice of the precursor, the products possess a chiral quaternary bridgehead aryl substitution. Also described is the diverse synthesis of 6-keto and 6-alkenyl carbohydrates by a general approach. The overall protocol provides versatility through the possibility of introducing diverse reagents at several entry points.

Homopolymerization and [2 + 4]/[3 + 2] cycloaddition in the reaction of nitroethylene with vinyl ethers

AbstractThe reaction of nitroethylene with isobutyl vinyl ether was reinvestigated. In agreement with the report of Kushibiki, Irie, and Hayashi (J Polym Sci Polym Chem Ed 1975, 13, 77), cycloaddition accompanied the anionic homopolymerization of nitroethylene. However, the cycloadduct was not a cyclobutane but a bicyclic oxazolidine, in keeping with the more recent report by Denmark and Hurd (J Org Chem 1998, 63, 3045). Cycloaddition accompanied by the anionic homopolymerization of nitroethylene was general for a series of vinyl and silyl ethers. Mechanistically, the cycloadducts formed by a cis–syn concerted approach of the reactants, whereas a trans–anti approach gave a zwitterionic tetramethylene that initiated anionic homopolymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1886–1891, 2001

Stereoselective synthesis of oxazolidines from 2-amino-2-deoxy- d-allose derivatives and their reactivity with nucleophiles

The use of 2-amino-2-deoxy- d-allose in the synthesis of oxazolidines is described. The reaction takes place with total stereoselectivity in the preparation of both simple oxazolidines (from aldehydes as reagent) and bicyclic oxazolidines (from chlorocarbonyl compounds and keto-acids as reagents). The reactivity of the obtained oxazolidines with hydride and alkylmagnesium chlorides is also described.

Diastereoselective alkylation of α-amino-substituted benzyllithiums

Reductive lithiation of a distereoisomeric mixture of bicyclic oxazolidines followed by reaction with alkyl halides afforded aminoalcohols in a highly syn-selective fashion. Reductive lithiation occurs with racemization at the benzylic carbon atom; the observed diastereoselectivities are rationalized in terms of a pair of rapidly equilibrating diastereoisomeric organolithium intermediates, one of which reacts preferentially under appropriate reaction conditions.