Showing papers in "Journal of Organic Chemistry in 1987"

Rothemund and Adler-Longo reactions revisited: synthesis of tetraphenylporphyrins under equilibrium conditions

Abstract: We present a new synthetic strategy for preparing tetraphenylporphyrins that should greatly expand synthetic entries into porphyrin containing model systems. Pyrrole and the desired benzaldehyde react reversibly at room temperature with trace acid catalysis to form the cyclic tetraphenylporphyrinogen at thermodynamic equilibrium. An oxidant is then added to irreversibly convert the porphyrinogen to the porphyrin. The greater stability of the cyclic porphyrinogen over the open-chain polypyrrylmethanes occurs when the reaction is performed at moderate dilution (10-2 M). The reaction at high dilution or high concentration affords a negligible yield of the cyclic porphyrinogen. Porphyrinogen exchange reactions provide proof of equilibrium. This methodology is complementary to the Adler-Longo procedure, allowing small quantities of porphyrins to be prepared from sensitive aldehydes in 30-40% yield without difficult purification problems. This methodology is also extended to the preparation of meso-tetraalkylporphyrins and one hybrid porphyrin containing both aryl and alkyl substituents. The mild reaction conditions and convenience of this method permit consideration of new design strategies in preparing complex porphyrins.

Fast and selective oxidation of primary alcohols to aldehydes or to carboxylic acids and of secondary alcohols to ketones mediated by oxoammonium salts under two-phase conditions

Abstract: General Oxygenation Procedure. An apparently heterogeneous mixture of an olefin (cyclohexene, 1-pentene, or styrene, 1 g), NaBH, (300 mg, 7.9 mmol), (OEP)RhnxCl (4.0 mg, 6 pmol; [Rh] = 0.6 mM), and an internal standard (p-xylene, mesitylene, or durene, appropriate amount) in dry THF (10 mL) exposed to dry air was stirred a t 20-25 \"C. The oxygenation of 1-methylcyclohexene was carried out by using the rhodium catalyst in an amount 2 or 20 times as much as that used above ([Rh] = 1.2 or 12 mM). The electronic spectra of the reaction mixture underwent no significant change even after 100 h. The formation of oxygenation products was monitored by gas chromatography. Similarly was carried out the oxygenation of 1,5-cyclooctadiene and acetylenes (1-heptyne and 3-heptyne) by using substrate (300 mg), NaBH, (300 mg), and (OEP)RhmC1 or (TPP)RhInC1 (4.0 mg) in THF (20 mL). Reaction products, after conversion if necessary to silylated derivatives, were identified by gas chromatography on the basis of coinjection with authentic samples, and their yields determined also by gas chromatography. 2-Methylcyclohexanol as a mixture of stereoisomers arising from the oxygenation of 1-methylcyclohexene was purified by preparative gas chromatography. The stereoisomer distribution was determined by 'H NMR spectroscopy by taking advantage of the characteristic signals for hydroxymethine protons a t 6 3.1 (for E isomer) and 3.75 (for 2 isomer). The following control runs were carried out by using cyclohexene as substrate: (1) without rhodium porphyrin catalyst, (2) without 02, (3) without NaBH,, and (4) with NaBH(OCHJ3 in place of NaBH,. In neither case was detected oxygenation of substrate to any significant extent. Another control run using cyclohexene oxide in place of cyclohexene under otherwise identical oxygenation conditions did not give cyclohexanol. Borane Transfer. A mixture of (0EP)Rh\"'Cl (40 mg, 0.06 mmol), NaBH4 (100 mg, 2.64 mmol), and 1-pentene (70 mg, 1.0 mmol) in T H F (2 mL) in a vessel sealed with a rubber septum was degassed by freezepumpthaw cycles and was stirred a t room temperature for 19 h. The electronic spectrum of the mixture showed A, a t 395,514, and 545 nm, indicating the formation of (OEP)RhH? Following the standard procedure for the analysis of organoboranes,28 the mixture was then subjected to gas chromatography at 170 OC on a column of silicone SE-30 (2 m), which had been treated with Silyl-8 (Pierce Chemical Co.) to mask protic sites with trimethylsilyl groups. The product was readily identified as tripentylborane on the basis of coinjection with the authentic sample prepared by hydroboration of olefin with diborane under standard conditions. The mixture was exposed to air, stirred for 20 min, and then analyzed by gas chromatography to show the formation of 1-pentanol and 2-pentanol (94:6, in a total yield of 45% based on mol of Rh complex used). Oxidation of Alkylborane. A T H F solution of (E)-bis(2methy1cyclohexyl)borane\" was prepared by the hydroboration of 1-methylcyclohexene (96 mg, 1.0 mmol) with borane-THF (1 M) (0.5 mL, 0.5 mmol) in THF (1 mL) under nitrogen. To this was added 1 N aqueous NaOH (0.5 mL), and the mixture was stirred under air atmosphere for 20 h. Gas chromatographic analysis using silicone DCQF-1 showed the formation of 2methylcyclohexanol with the stereoisomer ratio of E / Z = 7624. Another control run for the oxidation of alkylborane with O2 was carried out in the presence of NaBH, (38 mg, 1.0 mmol) instead of aqueous NaOH under otherwise identical conditions and gave the isomer ratio of E / Z = 81:19. A solution of (E)-bis(2-methylcyclohexyl)borane in THF (0.21 mL) was prepared as above starting from the olefin (15.4 mg, 0.16 mmol). This solution was added to (OEP)RhH15 (100 mg, 0.16 mmol) under nitrogen. The mixture was then allowed to contact with a gentle stream of THF-saturated air for 20 h. Gas chromatography coupled with 'H NMR analysis indicated almost exclusive formation of (E)-2-methylcyclohexanol.

Force-field model for intramolecular radical additions

Abstract: Ce modele permet de prevoir de facon precise la regioselectivite et la stereoselectivite des reactions de cyclisation des radicaux alkyles

The synthesis and configurational stability of differentially protected .beta.-hydroxy-.alpha.-amino aldehydes

Abstract: A partir de Boc-Ser-OMe ou de Boc-Thr-OMe et du dimethylacetal de l'acetone, via la reduction des dimethyl-2,2- et trimethyl-2,2,5 R-4 oxazolidinecarboxylates-3 de t-butyle (I) (R=methoxycarbonyl), obtention des composes I avec R=formyl

Asymmetric hydrogenation of unsaturated carboxylic acids catalyzed by BINAP-ruthenium(II) complexes

Abstract: Hydrogenation d'acides, d'hydroxyacides, et de diacides vinyliques. Application a la synthese du naproxene a partir de l'acide [methoxy-6 naphtyl-2]-2 acrylique

Intramolecular alkene arylations for rapid assembly of polycyclic systems containing quaternary centers. A new synthesis of spirooxindoles and other fused and bridged ring systems

Abstract: Exemples d'arylations intramoleculaires d'arenes halogenes o-substitues par un groupe insature

Hypervalent iodine oxidation of p-alkoxyphenols and related compounds : a general route to p-benzoquinone monoacetals and spiro lactones

Abstract: Oxydation de dimethoxy-, trimethoxy-, carboxy-2', ethyl, carboxy-2' ethoxy- et hydroxy-2' ethylphenols a l'aide du bis-trifluoroacetoxyiodo benzene

Spectral and chemical properties of dimethyldioxirane as determined by experiment and ab initio calculations

Abstract: It seemed to us, therefore, advisable to check our previous oxygen-transfer results' with the thianthrene 5-oxide (SSO) probe by employing the recently isolated6 dimethyl- dioxirane (2b). We used this opportunity to reinvestigate the spectroscopic properties of 2b and to compare these with the results of ab initio calculations carried out for 1, 2a,b, and appropriate reference compounds.

Synthesis of functionalized styrenes via palladium-catalyzed coupling of aryl bromides with vinyl tin reagents

Abstract: Copulation entre le (tributylvinyl) stannane et des bromoethers, bromoaldehydes, bromocetones et des composes dibromes benzeniques

A synthesis of protected aminoalkyl epoxides from .alpha.-amino acids

Abstract: Synthese d'α-aminoaldehydes (A) par reduction des aminoesters ou par oxydation des aminoalcools correspondants; par reaction de Wittig sur ces composes A, on obtient des α-alkyl allylamines N-protegees qui sont ensuite epoxydees

An assessment of the causes of the cesium effect

Abstract: Cesium alkanoates (chiefly the propionate) have been investigated for their solubility, nucleophilic reactivity, and degree of ion pairing in dimethylformamide (DMF) and, in some cases, dimethyl sulfoxide (DMSO) solutions. 133Cs NMR has been used to establish the degree of ion pairing. From the data obtained it is concluded that the cesium ion is virtually completely solvated and that the carboxylates are essentially free and highly reactive. The consequences of this effect on macrocyclization by means of nucleophilic substitution are discussed.

1,3-Dipolar cycloaddition reactions of pyrazolidinium ylides with acetylenes. Synthesis of a new class of antibacterial agents

Abstract: Cycloadditions d'ylures de t-butoxycarbonylamino-4 alkylidene-1 oxo-3 pyrazolidiniums et de composes acetyleniques: synthese de t-butoxycarbonylamino-2 tetrahydro-1,2,3,5 pyrazolo [1,2-a] pyrazolones-1; acylation de ces composes sur l'amino-2 par le chlorure d'acide allyloxycarbonylamino-2 α-methoxyimino thiazoleacetique-4

Oxidation of olefins and alcohols by peroxo−molybdenum complex derived from tris(cetylpyridinium) 12-molybdophosphate and hydrogen peroxide

Abstract: Le complexe peroxo du titre oxyde les olefines en epoxydes et les alcools en composes carbonyles avec de bons rendements

Methylenecyclopropane rearrangement as a probe for free radical substituent effects. .sigma..bul. Values for commonly encountered conjugating and organometallic groups

Abstract: Une serie d'aryl-3 dimethyl-2,2 methylene-1 cyclopropanes, avec en position para du cycle benzenique les groupes suivants: NO 2 , NMe 2 , vinyl, isopropenyl, phenyl, cyclopropyl, CH 2 SiMe 3 , SiMe 3 , SnMe 3 -BOCH 2 CH 2 O et HgCl, est preparee. Ces composes se transposent thermiquement en les isopropylidenecyclopropanes correspondants