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Hydrogenation of an imine (N-Cyclohexyl(benzylidene)imine) into a secondary amine (N-Benzylcyclohexylamine) was studied in catalyst-coated tube reactors to utilize the advantages of continuous-flow processes. Tetrahydrofuran (THF) was found to be an optimal solvent providing high reaction and low catalyst deactivation rates compared to toluene and isopropanol. Even in THF, however, the deactivation was noticeable, with a decrease in the imine hydrogenation rate of 80 and 47% during 20 h on stream over the Pd/C and Pd/SiO2 catalyst-coated tubes, respectively. After comparing various regeneration methods, we found that washing with isopropanol recovered the catalyst activity. The catalyst support affected regeneration: the Pd/SiO2 catalyst suffered from a permanent degradation, whereas the Pd/C was stable over multiple reaction-regeneration cycles. Process intensification study at a range of reaction temperatures allowed to establish the optimal secondary amine production temperature of 110 °C. The long-term stability test under the optimized conditions allowed reaching a turnover number (TON) of 150 000, an unprecedented value in heterogeneous imine hydrogenation. A reductive amination cascade reaction (aldehyde and amine condensation simultaneously with imine hydrogenation) showed the byproduct yield below 3%. The cascade reaction, however, decreased the reaction throughput by 45% compared to the direct imine hydrogenation still allowing for a throughput of 0.75 kg of product per day in a single 5 m catalyst-coated reactor opening a way for a multikilogram synthesis.\ud \ud

Composite NiFe2O4–TiO2 magnetic catalysts were prepared by mechanochemical synthesis from a mixture of titania supported nickel ferrite nanoparticles and P25 titania (Evonic). The former provides fast and efficient heating under radiofrequency field, while the latter serves as an active catalyst or catalyst support. The highest heating rate was observed over a catalyst prepared for a milling time of 30 min. The catalytic activity was measured over the sulfated composite catalysts in the condensation of aniline and 3-phenylbutyric acid in a stirred tank reactor and in a continuous RF heated flow reactor in the 140–170 °C range. The product yield of 47% was obtained over the sulfated P25 titania catalyst in the flow reactor.

Induction of mild states of hyperketonemia may improve physical and cognitive performance. In this study, we determined the kinetic parameters, safety and tolerability of (R)-3-hydroxybutyl (R)-3-hydroxybutyrate, a ketone monoester administered in the form of a meal replacement drink to healthy human volunteers. Plasma levels of β-hydroxybutyrate and acetoacetate were elevated following administration of a single dose of the ketone monoester, whether at 140, 357, or 714 mg/kg body weight, while the intact ester was not detected. Maximum plasma levels of ketones were attained within 1–2 h, reaching 3.30 mM and 1.19 mM for β-hydroxybutyrate and acetoacetate, respectively, at the highest dose tested. The elimination half-life ranged from 0.8–3.1 h for β-hydroxybutyrate and 8–14 h for acetoacetate. The ketone monoester was also administered at 140, 357, and 714 mg/kg body weight, three times daily, over 5 days (equivalent to 0.42, 1.07, and 2.14 g/kg/d). The ketone ester was generally well-tolerated, although some gastrointestinal effects were reported, when large volumes of milk-based drink were consumed, at the highest ketone monoester dose. Together, these results suggest ingestion of (R)-3-hydroxybutyl (R)-3-hydroxybutyrate is a safe and simple method to elevate blood ketone levels, compared with the inconvenience of preparing and consuming a ketogenic diet.

Radical reaction of a series of N-(2-bromoallyl)arylcarboxamides led to the production of 4-arylpyrrolidin-2-ones and directly reduced materials in comparable yields. A cascade process, involving sequential 5-exo-trig spirocyclisation, β-scission, and 5-endo-trig cyclisation of the resulting acyl radical, is proposed to explain the pyrrolidinone products. © 2006 Elsevier Ltd. All rights reserved.

A tricyclic core structure 2 related to gelsemine 1 was synthesized from an oxabicyclo[3.2.1]octanone 4 by a three-step bridge swapping strategy involving elimination of the bridging ether oxygen and intramolecular Michael addition of a tethered cyanoacetamide unit.

N-Tosyl-5,5-divinyloxazolidin-2-one undergoes a palladium-catalyzed decarboxylative cyclization across a range of electrophilic alkenes to give the corresponding pyrrolidine derivatives bearing two contiguous quaternary centres. Alkenes bearing two electron-withdrawing groups are required; pyrrolidines were not formed from mono-activated alkenes. Bulky, electron-rich phosphines promote pyrrolidine formation with less highly electrophilic, doubly activated alkenes, and a dramatic improvement is observed in the presence of iodide.

On heating in toluene at 180 °C for four days the TMS enol ether 7 underwent a domino acid catalysed rearrangement, Diels–Alder cycloaddition and further rearrangement to give the bicyclic TMS enol ether 17, which was converted into a tetrodecamycin precursor 3 in three synthetic steps. Further, monocyclic silyl enol ethers were consecutively treated with mCPBA and bromine to give syn α-hydroxy α′-bromo ketones in a one-pot reaction sequence. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

On treatment with trifluoroacetic acid the tetraene precursor 23 underwent Boc deprotection, condensation and an iminium ion accelerated intramolecular Diels-Alder cycloaddition resulting in an iminium species 12, which was further converted into himbacine 1, himbeline 3 and himandravine 4, three out of four Galbulimina type I alkaloids thus providing strong evidence for the proposed biogenesis of this important family of alkaloids.

Glycine-derived N-tosyl-5,5-divinyloxazolidin-2-one 10 undergoes a palladium catalysed decarboxylative ring-opening cyclization with strongly electron deficient alkylidenemalonate derivatives to give highly substituted pyrrolidines 14 containing two contiguous quaternary centres.

Spirolactams were obtained via an intramolecular radical ipso-type spirocyclisation in benzofuran and indole systems. Alkyl, vinyl and aryl radicals, tethered at the C-2 position of the heterocycle underwent radical cyclisation to produce novel tricyclic partially dearomatised heterocycles in moderate yields. Fragmentation of the furan ring was observed subsequent to spirocyclisation of a vinyl radical onto a benzofuran.

In a short sequence, 5-vinyloxazolidin-2-ones were converted into the 3,6-disubstituted 3,6-dihydropyridin-2-ones via Pd-catalysed carbonylation and enolate alkylation with high diastereoselectivity. Alkylation of 6-substituted N -methylpyridin-2-ones gives stereoselectively the 3,6- anti diastereoisomer with MeI, BuI and i -PrI. Alkylation of the corresponding N -BOC pyridinones gives the 3,6- syn diastereoisomer with high selectivity.

The stereoselective synthesis of piperidine alkaloids deoxymannojirimycin and d -mannolactam from d -serine has been achieved. The key step involves palladium-catalysed decarboxylative carbonylation of a serine-derived 5-vinyloxazolidin-2-one to give 6-(tert-butyldimethylsilyloxymethyl)-3,6-dihydro-1H-pyridin-2-one which was subsequently converted into the title compounds.

(Ph 3 P) 2 PdCl 2 was found to be the most effective of a range of catalysts for decarboxylative carbonylation of (4 S ,5 RS )-5-ethenyl-4-(2-propyl)oxazolidin-2-one to give the δ-lactam, (6 S )-3,6-dihydro-6-(2-propyl)-1 H -pyridin-2-one. In a similar way, diastereoisomerically pure (4 S ,5 S )-4-benzyl-5-(( Z )alk-1-enyl)oxazolidin-2-ones undergo stereospecific carbonylation to give (3 R ,6 S )-6-benzyl-3-alkyl-3,6-dihydro-1 H -pyridin-2-ones. The diastereoisomeric (4 S ,5 R )-4-benzyl-5-(( Z )alk-1-enyl)oxazolidin-2-ones give rise to a separable mixture of the corresponding (3 S ,6 S )-6-benzyl-3-alkyl-3,6-dihydro-1 H -pyridin-2-one and (4 S ,5 S )-4-benzyl-5-(( E )alk-1-enyl)oxazolidin-2-one. Under more forcing conditions, the latter oxazolidinone is carbonylated to the 3,6- anti -pyridinone. The stereochemical course of the reactions can be rationalized by formation of a π-allyl palladium cation with inversion of configuration followed by carbonylation with retention. The stereospecificity observed in our system precludes metal–metal exchange of the π-allyl complexes by a Pd(0) displacement process.

Chiral lithium amide bases are able to deprotonate N-benzyl-N-cumyl anisamides enantioselectively to yield enantiomerically enriched benzylic organolithiums. These spontaneously undergo dearomatising cyclisation to yield, in high enantiomeric excess enantiomerically enriched partially saturated isoindolones, which in some cases may be recrystallised to enantiomeric purity. These isoindolone derivatives are converted in nine steps, among them a surprisingly regioselective Baeyer–Villiger reaction, to (−)-kainic acid.

Dearomatising anionic cyclisation of N -cumyl- N - p -methoxybenzyl-4-methoxy-1-naphthamide 8 diastereoselectively generates a pyrrolidinone-fused tetralone 12 which may be transformed in seven steps to the racemic form of a known non-natural member of the aryl kainoid family 4 having potent biological activity. Key steps of the synthesis are ruthenium-catalysed oxidation of the C2- p -methoxybenzyl ring of 12 to a carboxylic acid and Baeyer–Villiger cleavage of the tetralone to a lactone whose hydrolysis reveals the two-carbon substituent at C3 and the 2-hydroxyphenyl substituent at C4. Selective reduction of the lactam yields the kainoid 4 . Control of epimerisation at the C-4 centre during the lactone hydrolysis leads to either the (active) 3,4- cis or the (inactive) 3,4- trans epimers of the target.

The tropolone subunit of the naturally occurring alkaloid rubrolone aglycon is synthesized via a short reaction sequence starting with a 1,3-dipolar cycloaddition of a pyrylium ylide and indenone, followed by enone oxidation, oxygen-bridge elimination and finally hydroxy group oxidation.

The direct and solvent-free formation of amides from carboxylic acids and amines using radiofrequency heating is reported.

Chiral enamides 5f–i were found to react with pyrylium ylides to give cycloadducts 6d–i in good yields with an excellent level of stereoselectivity. The chiral auxiliary was successfully removed on hydrogenolysis of compound 6f in continuous flow (H-Cube) resulting in the first asymmetric synthesis of complex amine 8.

On treatment with t-BuLi in presence of HMPA, methoxybenzamides, e.g. I (Ar = Ph, 4-MeOC6H4), cyclized with dearomatization to give Me dienyl ethers, e.g. II, which were hydrolyzed with dil. HCl to give single stereo- and regioisomers of pyrrolidine-fused cyclohexenones, e.g. III. The bicyclic enones are versatile synthetic intermediates which undergo transformations such as stereoselective redn. and conjugate addn., regioselective Baeyer-Villiger oxidn., bromination and hydrogenation. [on SciFinder (R)]

N-Tosyl-5,5-divinyloxazolidin-2-one undergoes a palladium-catalyzed decarboxylative cyclization across a range of electrophilic alkenes to give the corresponding pyrrolidine derivatives bearing two contiguous quaternary centres. Alkenes bearing two electron-withdrawing groups are required; pyrrolidines were not formed from mono-activated alkenes. Bulky, electron-rich phosphines promote pyrrolidine formation with less highly electrophilic, doubly activated alkenes, and a dramatic improvement is observed in the presence of iodide.

This Letter has been retracted, as it was found that (a) spectra of the linear precursor, compound 14, differed when its synthesis was repeated and (b) spectra published for several compounds resulting from compound 14 (compounds 3, 4, and 20) were scanned from other papers. Compounds 3 and 20: Chackalamannil, S.; Davies, R. J.; Asberom, T.; Doller, D.; Leone, D. J. Am. Chem. Soc. 1996, 118 (40), 9812−9813; Chackalamannil, S.; Davies, R. J.; Wang, Y.; Asberom, T.; Doller, D.; Wong, J.; Leone, D.; McPhail, A. T. J. Org. Chem. 1999, 64 (6), 1932−1940. Compound 4: Chackalamannil, S.; Davies, R.; McPhail, A. T. Org. Lett. 2001, 3 (10), 1427−1429.

Linked bis-pyrazoles, a pyrazolyl-isoxazole, a pyrazolyl-pyrimidine and a pyrazolyl-triazole were synthesized starting with commercially available 1,4-bis(trimethylsilyl)-1,3-butadiyne 1 or readily available bis-acetylenic diketone 22 . A stepwise approach based on the use of 1 allowed the synthesis of nonsymmetrically substituted bis-pyrazoles and linked heterocycles with two different cores whereas a symmetric approach based on the use of 22 allowed a very short synthesis of symmetric bis-pyrazoles.

On treatment with trifluoroacetic acid the tetraene precursor 23 underwent Boc deprotection, condensation and an iminium ion accelerated intramolecular Diels-Alder cycloaddition resulting in an iminium species 12, which was further converted into himbacine 1, himbeline 3 and himandravine 4, three out of four Galbulimina type I alkaloids thus providing strong evidence for the proposed biogenesis of this important family of alkaloids.

This Letter has been retracted, as it was found that (a) spectra of the linear precursor, compound 14, differed when its synthesis was repeated and (b) spectra published for several compounds resulting from compound 14 (compounds 3, 4, and 20) were scanned from other papers. Compounds 3 and 20: Chackalamannil, S.; Davies, R. J.; Asberom, T.; Doller, D.; Leone, D. J. Am. Chem. Soc. 1996, 118 (40), 9812−9813; Chackalamannil, S.; Davies, R. J.; Wang, Y.; Asberom, T.; Doller, D.; Wong, J.; Leone, D.; McPhail, A. T. J. Org. Chem. 1999, 64 (6), 1932−1940. Compound 4: Chackalamannil, S.; Davies, R.; McPhail, A. T. Org. Lett. 2001, 3 (10), 1427−1429.

On treatment with trifluoroacetic acid butenolide 14 undergoes N-Boc deprotection and condensation followed by an iminium ion activated intramolecular Diels-Alder cycloaddition to give the (+)-himbacine precursor 11 on reductive work up. Compound 11 was converted into (+)-himbacine in four synthetic steps. [reaction: see text]

N-Benzyl p-anisamide 6, on lithiation with ButLi in the presence of HMPA, undergoes a stereoselective anionic cyclisation with loss of aromaticity to give a bicyclic enone which may be converted in nine steps to (±)-kainic acid.

Starting from a protected L-tryptophan derivative the pyrrolobenzoxazine core unit of paeciloxazine can be synthesized in two oxidation steps.