Cyclopropanation reactions with α, β-epoxy diazomethyl ketones and rearrangement of α, β-epoxy cyclopropyl ketones

The cyclopropanation reactions of α, β-epoxy diazomethyl ketones 1 with olefins using Pd(OAc)₂ as catalyst is described. Differently substituted epoxy diazo ketones 1a-1f give with cyclohexene exo-norcarane derivatives. 3, 3-Diphenyloxiranyl-2 diazomethyl ketone 1a reacts with olefins like isobutene, E- and Z- butene-2 to give epoxy cyclopropyl ketones. 3, 3-Diphenyloxiranyl-2 cyclopropyl ketones 2a and 9 undergo two consecutive rearrangement reactions with BF₃ as catalyst. In the first step an epoxide rearrangement of 9 takes place to give β-ketoaldehyde 10, which in a second step rearranges to enolester 12. The latter reaction is most likely restricted to β-ketoaldehydes which have a quaternary α-C atom. A rationale for this unusual reaction has been proposed.     

An efficient synthesis of benzofurans and their application in the preparation of natural products of the genus Calea

The intramolecular cyclization of the β-substituted olefins methyl 2-aryloxy-3-dimethylaminopropenoates 3a-3f catalyzed by Lewis acids leads to a short and novel synthesis of benzofurans 2a-2f. When the olefins 4-dimethylamino-3-aryloxy-3-buten-2-ones 4a-4f were used, the cyclization process was faster and provided the corresponding substituted 2-acetylbenzofurans 1a-1f. Among the latter, naturally occurring compounds calebertin (1a), caleprunin A (1b), and caleprunin B (1c) were prepared in good overall yields. These benzofurans were also obtained by direct treatment under MW irradiation of the precursors 1-aryloxypropan-2-ones 7a-7c with DMFDMA, followed by addition of the catalyst, resulting in a route that was one step shorter.     

Captodative olefins: methyl 2-aryloxy-3-dimethyl-aminopropenoates and their application in a new synthesis of benzofurans

The β-substituted captodative olefins methyl 2-aryloxy-3-dimethylaminopropenoates 4a-h were synthesized, via aminomethylenation of the corresponding 2-phenoxyacetic esters 9a-h. Lewis acid promoted intramolecular cyclization of alkenes 4 led to benzofurans 7a-h, in an efficient synthetic approach to the benzofuran frame.     

Fine-tunable monodentate phosphoroamidite and aminophosphine ligands for Rh-catalyzed asymmetric hydroformylation

A biaryl-based monophosphoroamidite L1–L4a–f and aminophosphine L5–L7a–f ligand library was screened in the Rh-catalyzed asymmetric hydroformylation of several vinylarenes and heterocyclic olefins. Our results indicate that the selectivity is strongly dependent on the ligand parameters and on the substrate type. Enantioselectivities (up to 46%) were moderate in the hydroformylation of several vinylarenes S1–S5 and promising (up to 58%) for the more challenging heterocyclic olefins S6–S9.     

“Olefin metathesis” reactions of (η5-C5H5)NiRu3(μ-H)(CO)9-(μ4-η2)-(CCHBut) and related complexes

The complex (η⁵-C₅H₅)NiRu₃(μ-H)(CO)₉(μ₄-η²-CCHBu^t) (1a) reacts with olefins to give several organic products, including species derived from the coupling of the vinylidene ligand with an olefin-derived =CRR′ fragment, representing the first example of a (non catalytic) olefin metathesis reaction involving a metal cluster; other complexes structurally or chemically related to the compound 1a have also been treated with olefins and alkynes.     

2,4,6-Tri-isopropylbenzenesulphonyl hydrazide: A convenient source of di-imide

2,4,6-Tri-isopropylbenzenesulphonyl hydrazide (TPSH, 3a) undergoes thermal decomposition in d₄-methanol solution at 35°, in the presence of triethylamine, at a rate ca. 380 times that of p-toluenesulphonyl hydrazide (2b). 3a has been found to be a convenient and effective hydrogenating agent for azobenzene and a number of olefins in methanol solution at 20° and in boiling ether and tetrahydrofuran solutions. Reductions in ether solution appear to be facilitated by the addition of base. 2,4,6-Trimethylbenzenesulphonyl hydrazide (MSH, 4a) undergoes thermal decomposition at a rate ca. 24 times that of 2b; 4a is also a useful hydrogenating agent.     

Synthesis of 1,3-diaryl-1H-benzo[g]indazoles

A facile three-step synthetic route toward 1,3-diaryl-1H-benzo[g]indazoles 1a–1n starting with 3,4-dimethoxy-2-allylbenzaldehyde (6) in modest total yield is described. The facile route was carried by aldol condensation of aldehyde 6 with aryl methyl ketones 5a–5d in alkaline MeOH at reflux, Knorr pyrazole synthesis of the resulting chalcones 4a–4d with aryl hydrazines 3a–3e in EtOH at reflux followed by DDQ-mediated aromatization in toluene at reflux, and oxidative cleavage annulation of olefins 2a–2n with the one-pot combination of OsO₄/NaIO₄/HOAc in the aqueous THF at reflux.     

Asymmetric epoxidation of olefins by chiral dioxiranes generated in situ from ketones of d-(−)-quinic acid

The in situ generated dioxiranes (Caroate as peroxide source) of the optically active ketones 4a and 4b, which may be conveniently prepared from d-(−)-quinic acid, serve as effective oxidants for the asymmetric epoxidation (ee values up to ca. 90% with 4a) of prochiral olefins.     

Palladium-catalyzed oxyarylation of olefins using silver carbonate as the base. Probing the mechanism by electrospray ionization mass spectrometry

The Pd(OAc)₂-catalyzed oxyarylation of electron-rich (8 and 12) and electron-poor (10) olefins by ortho-iodophenols (3a-d) was studied using Ag₂CO₃ as the base, in acetone, and in the presence and absence of PPh₃. The corresponding adducts of oxyarylation were obtained in moderate yields. The reaction mechanism was examined by electrospray ionization mass spectrometry (ESI-MS). Cationic arylpalladium intermediate (14), formed by the oxidative insertion of Pd(0) into 3a, and the cationic palladacycles (15), obtained by reaction of 14 with olefins 8 and 12, were intercepted by ESI-MS and characterized by ESI-MS/MS.     

Nucleophilic addition to nitroacrylates: application towards the synthesis of 2,3-dehydroamino acids and 2,3-diamino acids

The addition of the N-pronucleophiles to 2- or 3-nitro-2-alkenoates in the presence of base provided Michael addition products. In the case of 3-nitro compounds, reaction occurred via the formation of α-adducts and the subsequent elimination of nitrous acid to produce olefins with high Z stereoselectivity. 3-Phthalimido-2-nitrocinnamate adduct 8a was converted into 2,3-diamino ester 11a.     

Asymmetric hydrogenation reactions with Rh and Ru complexes bearing phosphine–phosphites with an oxymethylene backbone

Phosphine–phosphites 3a and 3b, derived from diphenylhydroxymethyl phosphine have been prepared. From these ligands [Rh(COD)(3a)]BF₄ 5a and RuCl₂(3b)[(S,S)-DPEN] 6b (DPEN = 1,2-diphenylethylenediamine) were synthesized and their structure determined by X-ray diffraction. Ligands 3 are characterized by a small bite angle of 83°. In addition, 5a led to an active catalyst for the hydrogenation of olefins, giving enantioselectivities of up to 96% ee. Likewise, compound 6b showed good activity and enantioselectivity in the hydrogenation of N-1-phenyl ethylidene aniline and a completed reaction at S/C = 500 in 24 h with 83% ee.     

Synthesis of chiral 4-substituted 2-hydroxypent-4-enoic acid derivatives via diastereoselective ene reaction promoted by ZnBr2

The diastereoselective carbonyl-ene reaction of various 1,1-disubstituted olefins with the chiral derivatives of glyoxylic acid, with Oppolzer’s sultam 1a and 8-phenylmenthol 1b auxiliaries, was studied. The reaction proceeds effectively under undemanding conditions in the presence of equimolar or catalytic amount of ZnBr₂ in good yield and at 72–94% de. Diastereoselectivities are usually slightly better with 8-phenylmenthyl glyoxylate 1b, however, the use of hemiacetal 1a is preferred because the products are often crystalline.     

High diastereoselective synthesis of spiro-barbituratechromans via domino oxa-Michael/1,6-addition reactions of ortho-hydroxyphenylsubstituted para-quinone methides with barbiturate-based olefins

A novel Et₃N-catalyzed domino oxa-Michael/1,6-addition reaction of ortho-hydroxyphenylsubstituted p-QMs with barbiturate-based olefins is achieved under mild conditions. Various new spiro-barbituratechromans were obtained in excellent yields and diastereoselectivities (90–99% yield, >99:1 dr). The structure of the new compound 3a was determined by single crystal X-ray analysis.     

Palladium-catalyzed regioselective Heck arylation of electron-rich olefins in a molecular solvent-ionic liquid cocktail

We have recently established that highly regioselective Heck arylation of electron-rich olefins can be accomplished with aryl halides without using any halide scavengers in imidazolium ionic liquid solvents. The results presented in this paper show that the benchmark electron-rich olefins vinyl ethers can be readily arylated by aryl bromides in a molecular solvent-ionic liquid cocktail with no compromise on regioselectivity. By introducing a small amount of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) to DMSO, the arylation reactions of the vinyl ethers 1a-d by the bromides 2a-j took place to afford essentially only the α arylated products. The enamide 1e underwent similar regioselective arylation in the solvent cocktail. In the absence of the ionic liquid, lower regioselectivities were observed. In comparison with the chemistry we have reported so far, the current method reduces considerably the reliance on the volume of ionic liquids used, providing a simpler and more practical synthetic pathway for preparing arylated vinyl ethers and aryl methyl ketones.     

C-nitroso compounds—XXXI: The addition of α-chloronitroso compounds to olefins containing allylic hydrogen

α Chloronitrosoadamantane 1a gives upon reaction with 2-phenylpropene at room temperature virtually quantitatively a stable ketonitrone salt, the α,α-adamantylidene-N-(2-phenyl)prop-1-en-3-yl nitrone hydrochloride 2a. Evidence for the structure of the crystalline product is based on microanalytical data and spectroscopic properties, together with degradation studies. Similar aliphatic ketonitrone hydrochlorides have been obtained from reaction of 2-phenylpropene with other α-chloronitroso compounds 1b-1e (73–91%), and from α-chloroni-trosoadamantane . and a series of allylic olefins (76–95%). Rearrangement of an intermediary N-α-chloroalkyl-N-alkenylhydroxylamine, which has been initially formed by an ene-type process between the reactants, can explain formation of the product.     

Addition of carbon nucleophiles to cyclic N-acyliminium ions in SDS/water

The acid-catalyzed addition of 1,3-dicarbonyl compounds and activated olefins (silyl enol ethers and ethyl vinyl ether) to N-Boc-2-methoxypyrrolidine (1a) and N-Boc-2-methoxypiperidine (1b) in SDS/water medium is described. Good yields of the corresponding 2-substituted N-Boc pyrrolidines were generally observed from 1a while moderate yields prevailed from 1b.     

Ketene-S,S,-acetals—VI : Synthesis of 3,3-bis-(methylthio)-2-propene-2-alkyl-1-aryl-1-ones and their reaction with guanidine: A novel route for pyrimidine synthesis

The α-ketoketene-S,S,-acetals 2a–h have been synthesized from the appropriate ketones 1a–f in good yields by extending the established method. The acetals 2a–d react with guanidine in the presence of sodium ethoxide to give pyrimidines 4a–d in 35–59% overall yields (Scheme 1). Treatment of 2e with guanidine similarly gave 5a in 23% yield. However, the reaction of 2e with guanidine in the presence of sodium n-propoxide gave a mixture of three products from which 5a was isolated as major product (20%) with 6a (7%) and 7a (5%). Under similar reaction conditions, 2f gave 5b, 6b and 7b in identical yields. Treatment of 2g–h with guanidine in the presence of sodium n-propoxide gave only 8a (28%) and 8b (23%) respectively. The formation of these pyrimidines involves base induced 1,3-proton migration in 2a–h to give intermediate olefins 10a–h.     

Rh(II)-Catalyzed asymmetric carbene transfer with ethyl 3,3,3-trifluoro-2-diazopropionate

The asymmetric cyclopropanation of 1,1-diphenylethylene (2) with ethyl 3,3,3-trifluoro-2-diazopropionate (1) in the presence of chiral Rh(II) catalysts affords cyclopropane 3 with yields and enantioselectivities of up to 72 and 40%, respectively. Similar results are obtained for asymmetric cyclopropenation of hex-1-yne (4), although enantioselectivity is lower. The cyclopropanation of mono-substituted olefins (8a-8e) with 1 leads to cis/trans-mixtures of cyclopropanes 9a-9e with a maximum ee of 75% for 4-methoxystyrene (8c).     

A regioselective synthesis of daunomycinone and related anthracyclinones

The phthalic anhydrides 4a and 4b are attacked by the Grignard reagents 15 and 33 in tetrahydrofuran/tetramethylethylene diamine almost exclusively at the carbonyl group, which is situated in the meta position of the methoxy substituent(s). This highly regioselective reaction (minimum: 95:5) is used as the key step in a short synthesis of daunomycinone (2a), 2-methoxy-7-deoxycarminomycinone (22b),γ-rhodomycinone (8), and 10-dexoy-γ-rhodomycinone (9). The products of the addition of 15 to 4a and 4b, the pseudoacids 16 are converted via the olefins 17 and the epoxides 18 into the ketones 19, which lead by application of known reactions to the anthracyclinones 2a, 22a, and 9. The product, formed by addition of 33 to 4a, is converted to γ-rhodomycinone (8) via the quinone 27. The precursors of the Grignard reagents 15 and 33, the bromides 14 and 32, can be prepared easily and in large scale from the carboxylic acid 10, which is readily available from the cheap chemicals hydroquinone and succinic anhydride.     

Synthesis and highly selective Diels-Alder cycloadditions of the new dienes N-substituted 2,3,5,6-tetrahydrobenzoxazol-2-ones

The synthesis of the new dienes N-substituted 2,3,4,5-tetrahydrobenzoxazol-2-ones 8a-8c is described, through a one-step convergent process from 1,2-cyclohexanedione (7a) and the corresponding isocyanates 2a-2c. The presence of electron-donor substituents in the aryl ring of the isocyanate gave rise to the exclusive formation of the captodative olefins 10. Diene 8a proved to be reactive and stereoselective in Diels-Alder additions with a cyclic olefin. The reaction with acetylenic dienophiles yielded the 2,3-dihydrobenzoxazol-2-ones 21 and 24, as the products of sequential [4+2] cycloaddition and retro-Diels-Alder reactions. Methyl vinyl ketone (22) underwent regio- and stereoselective tandem Diels-Alder and Michael additions to give propellane 29a. Evidence of an endo π-pyramidalization of the central double bond of adduct 19 would rationalize the exo stereoselection in the formation of 29a. The regioselectivity in these reactions has been rationalized in terms of FMO theory by ab initio calculations.