Magnesium bromide mediated highly diastereoselective heterogeneous hydrogenation of olefins

Palladium on carbon combined with magnesium bromide catalyzed hydrogenation of Baylis-Hillman olefins to afford the corresponding aldol derivatives in a highly syn-diastereoselective manner is described. [reaction: see text]     

A general synthesis of 2,5-diaryl-4-chloro (or bromo)oxazoles

Reaction between acyleyanides (ArCOCN) and aldehydes (ArCHO) in the presence of ether and hydrogen chloride (or hydrogen bromide) gives good yields of 2,5-diaryl-4-chloro (or bromo)oxazoles ( 2 ).     

Reaction of perfluoroisobutylene with aromatic aldehydes

Conclusions Depending on the nature of the catalyst, 1,1-bis(trifluoromethyl)-2-arylethylenes or products of the addition of the perfluoro-tert-butyl anion to the carbonyl group are formed in the reaction of perfluoroisobutylene with ArCHO under conditions of nucleophilic catalysis.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1367–1371, June, 1981.     

Diastereo- and enantioselective total synthesis of stigmatellin A

Stigmatellin A (1) isolated from the myxobacterium Stigmatella aurantiaca is a powerful inhibitor of electron transport in mitochondria and chloroplasts. The first highly diastereo- and enantioselective total synthesis of this important natural product is described. Key steps in the synthesis are the alkylation of the SAMP-hydrazone (S)-13, a titanium mediated syn-diastereoselective aldol reaction, the anti-diastereoselective triacetoxyborohydride reduction of the aldol adduct (R,R,S)-16, formation of the chromone system via Baker Venkataraman rearrangement and exclusive (E) C=C double bond formation via Horner-Wadsworth-Emmons reaction.     

Asymmetric ethylation of aromatic aldehyde by diethylzinc in the presence of chiral auxiliaries derived from (S)-[4-HOC6H4CH2CH(NH2)CPh2OH]

A comparative study has been carried out on enantioselective ethylation of aromatic aldehydes (ArCHO) by diethylzinc (Et₂Zn) in the presence of catalytic amounts of (S)-[4-HOC₆H₄CH₂CH(NH₂)CPh₂OH] (1) or chiral auxiliaries derived from (1). Various procedures have been adopted; these involved (i) different sequences of addition of the reagents ArCHO, Et₂Zn and (1), and (ii) use of titanium(IV)isopropoxide [Ti(OPrⁱ)₄] or the boranetetrahydrofuran addition compound (BH₃ · THF) as additional reagents. In all but one of the procedures adopted, (S)-ArCH(OH)Et was selectively formed; enantiomeric excess values up to 87% were obtained.     

Diastereo- and Enantioselective Reductive Aldol Addition of Vinyl Ketones via Catalytic Hydrogenation

An overview of studies on hydrogenative reductive aldol addition is presented. By simply hydrogenating enones in the presence of aldehydes at ambient temperature and pressure, aldol adducts are generated under neutral conditions in the absence of any stoichiometric byproducts. Using cationic rhodium complexes modified by tri(2-furyl)phosphine, highly syn-diastereoselective reductive aldol additions of vinyl ketones are achieved. Finally, using novel monodentate TADDOL-like phosphonite ligands, the first highly diastereo- and enantioselective reductive aldol couplings of vinyl ketones were devised. These studies, along with other works from our laboratory, demonstrate that organometallics arising transiently in the course of catalytic hydrogenation offer byproduct-free alternatives to preformed organometallic reagents employed in classical carbonyl addition processes.     

富电子芳烃的电子转移光氧化反应

9,10-二氰蒽(DCA)敏化的烯烃和某些小环化合物的电子转移光氧化反应近年来研究很活跃。在芳烃光氧化方面,单重态氧反应限于多环芳烃和高度富电子的苯衍生物。一般烷基苯和富电子程度较小的芳烃,对~1O_2为隋性。因而电子转移历程为芳烃光氧化反应提供了新途径。但迄今芳烃的电子转移光氧化仍研究较少,历程看法也存在分歧。本文报道DCA和四氯对苯二醌(TCBQ)敏化的邻、间、对二甲苯(1,2,3),对-甲氧基     

Cobalt-catalyzed partial oxidation of olefins and ethers using molecular oxygen

Co(acac)₃ catalyzes the aerobic oxidation of vinyl aromatic compounds ArCH=CH₂ with formation of ArCO₂H and ArCHO, and also the aerobic oxidation of cyclic ethers with formation of the corresponding lactones.     

Reaction of diazonium salts with transition metals : X. Formylation of arenediazonium salts with carbon monoxide and silyl hydrides under palladium catalysis

Arenediazonium tetrafluoroborates (ArN₂BF₄ where Ar = X-C₆H₄; X = H, 2-Me, 3-Me, 4-Me, 4-MeO, 4-MeCO, 4-EtOCO, 2-Ph, 2-Cl, 3-Cl, 4-Cl, 4-Br, 4-I, 3-NO₂ and 4-NO₂) were easily converted to aromatic aldehydes (ArCHO) in good yields through the palladium-catalyzed reaction with CO and Et₃SiH or polymethylhydrosiloxane (PMHS) at room temperature.     

Efficient reductive selenation of aromatic aldehydes to symmetrical diselenides with Se/CO/H(2)O under atmospheric pressure

An efficient method for the synthesis of symmetrical diselenides is described. Reductive selenation of aromatic and heterocyclic aromatic aldehydes (ArCHO) with Se/CO/H(2)O in DMF afforded diselenides (ArCH(2)SeSeCH(2)Ar) in yields up to 94% under atmospheric pressure without use of a base.     

The preparation and transformations of 2-aza-3-oxabicyclo [2.2.1] heptene hydrochloride

Reaction of 1- chloro 1- nitroso cyclohexane with excess freshly prepared cyclopentadiene in ether: ethanol gives the crystalline 2-aza 3 oxabicyclo (2.2.1) heptene hydrochloride (1) in 89%, yields. 2-Aza 3-oxabicyclo (2.2.1) heptene (2), generated in situ with pyridine can be acylated with a variety of acid chlorides and anhydrides, thus providing a novel and convenient route to diverse oxazabicycloheptenes. The free base 2 generated with NaHCO₃ in a two phase system, readily reacts with formalin leading to the Mannich base adduct 16, with PhNCS to the thiourea 19 and with i-AmONO to the nitroso compound 20. PGG → PGE type cleavage is observed on reaction of the in situ generated 2 with excess benzoylchloride, MsCl and TsCl. Surprisingly, the reaction of 1 with ArCHO in presence of pyridine gives N-α-chloroaryl compounds possessing a highly reactive halogen. Diimide reduction of 2 gives the parent oxazabicycloheptane system-related to PG-endoperoxides—which was characterized as the hydrochloride or the benzoyl derivative.     

THE EFFECT OF OXYGEN ON THE INCORPORATION OF MANGANESE,IRON AND COBALT INTO HEMATOPORPHYRIN IX IN GLACIAL ACETIC ACID

Abstract

The results of polarography studies for the reaction of hematoporphyrin IX with Mn(II), Fe(II) and Co(II) ion in acetic acid in the absence and the presence of oxygen are reported. The metal incorporation reaction in the presence of oxygen is quantitative for Mn and Co and incomplete for Fe. In the absence of oxygen, the Mn reaction does not proceed at all, whereas, both the Fe and Co reactions are quantitative.     

Convenient preparative method for synthesis of methyl (Z)-3-aryl-2-(carbobenzoxyamino)acrylates by Wittig—Horner reaction with the use of Et3N as a base

The Wittig—Horner reaction of CbzNHCH(CO₂Me)P(O)(OMe)₂ (1) with ArCHO (2) in the presence of Et₃N as a base affords methyl (Z)-3-aryl-2-(carbobenzoxyamino)acrylates (3) with high degrees of diastereoselectivity (Z)/(E) > 101. One recrystallization of the crude product is sufficient to obtain isomerically and chemically pure (Z)-3.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2218-2220, November, 1995.The authors are grateful to the Dupont company (USA) for financing this study     

Synthesis and NMR spectral study of some t(3)-aryl-r(2),c(4)-bisethoxycarbonyl-t(5)-hydroxy-c(5)-methylcyclohexanones

Six t(3)-aryl-r(2),c(4)-bisethoxycarbonyl-t(5)-hydroxy-c(5)-methylcyclohexanones (6-11) were synthesized by condensing ArCHO (Ar = Ph, p-O(2)NC(6)H(4), p-CH(3)OC(6)H(4), p-ClC(6)H(4), m-O(2)NC(6)H(4) and m-C(6)H(5)O(6)H(4)) with ethyl acetoacetate in the presence of methylamine and their (1)H and (13)C NMR spectra were recorded. (1)H-(1)H COSY and NOESY spectra were recorded for 6 and 7 and also HSQC and HMBC spectra for 6 and 8. Elemental analysis was carried out for all compounds. The mass spectrum was recorded for 8. All analytical data are consistent with the proposed molecular formulae. Analysis of NMR spectral data suggests that these compounds largely adopt chair conformations with the hydroxyl group occupying an axial orientation and all the other substituents occupying equatorial orientations. Long-range coupling (2-3 Hz) between the OH proton and the axial methylene proton at C-6 is observed in 6, 7, 8 and 11.     

Highly enantioselective reductive cyclization of acetylenic aldehydes via rhodium catalyzed asymmetric hydrogenation

Catalytic hydrogenation of acetylenic aldehydes 1a-12a using chirally modified cationic rhodium catalysts enables highly enantioselective reductive cyclization to afford cyclic allylic alcohols 1b-12b. Using an achiral hydrogenation catalyst, the chiral racemic acetylenic aldehydes 13a-15a engage in highly syn-diastereoselective reductive cyclizations to afford cyclic allylic alcohols 13b-15b. Ozonolysis of cyclization products 7b and 9b allows access to optically enriched alpha-hydroxy ketones 7c and 9c. Reductive cyclization of enyne 7a under a deuterium atmosphere provides the monodeuterated product deuterio-7b, consistent with a catalytic mechanism involving alkyne-carbonyl oxidative coupling followed by hydrogenolytic cleavage of the resulting oxametallacycle. These hydrogen-mediated transformations represent the first examples of the enantioselective reductive cyclization of acetylenic aldehydes.     

Effect of metal ions on the determination of semicarbazide hydrochloride with potassium bromate

Semicarbazide can be titrated quantitatively with potassium bromate in the presence of nickel(II), cobalt(III) and manganese(II) but copper(II) causes serious interference. The effects of copper ions on the reaction between potassium bromate and semicarbazide are investigated and the optimum conditions under which the reaction is quantitative are indicated.     

The reaction of sodium arsenite with sodium chlorite

Existing procedures for the standardisation of sodium chlorite solutions are critically examined and a suitable method detailed. The reaction between sodium chlorite and sodium arsenite solutions is discussed; reaction is quantitative in the presence of sodium bicarbonate and osmic acid as catalyst.     

Kinetische Analyse in der organischen Chemie

Zusammenfassung o-Chlornitrobenzol gibt mit Hydroxylamin und Alkali unter Erwärmen eine Farbreaktion; p-Chlornitrobenzol setzt sich jedoch nur in geringem Maß um. Aufgrund dieser Reaktion kann o-Chlor-neben p-Chlornitrobenzol nachgewiesen und bestimmt werden. Chlordinitrobenzol liefert mit Hydroxylamin eine Färbung ohne Erwärmen und kann somit neben Chlornitrobenzol nachgewiesen und bestimmt werden. Die quantitative Bestimmung wird auf kinetischem Wege durchgeführt.

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Summary o-Chloronitrobenzene gives a colour reaction with hydroxylamine when warming in alcoholic caustic alkali solution, but p-chloronitrobenzene reacts only to a slight extent. This permits the detection or determination of o-chloronitrobenzene in the presence of p-chloronitrobenzene. Chlorodinitrobenzene yields a colour reaction with hydroxylamine without warming; on this basis it is possible to detect or determine chlorodinitrobenzene in the presence of chloronitrobenzene. A kinetic method is employed for the quantitative determination.

     

Regio- and diastereocontrol in carbonyl allylation by 1-halobut-2-enes with Tin(II) halides

Regio- and diastereoselective carbonyl allylations of 1-halobut-2-enes with tin(II) halides are described. Tin(II) bromide in a dichloromethane-water biphasic system is an effective reagent for unusual alpha-regioselective carbonyl allylation of 1-bromobut-2-ene to produce 1-substituted pent-3-en-1-ols. The addition of tetrabutylammonium bromide (TBABr) to the biphasic system produces 1-substituted 2-methylbut-3-en-1-ols via usual gamma-addition which is opposite to the alpha-addition without TBABr. The gamma-addition to aromatic aldehydes exhibits anti-diastereoselectivity, while that to aliphatic aldehydes is not diastereoselective. The allylation of benzaldehyde by 1-chlorobut-2-ene in 1,3-dimethylimidazolidin-2-one (DMI) does not occur with tin(II) chloride or bromide but does proceed with tin(II) iodide and exhibits gamma-syn selectivity which is unusual for a Barbier-type carbonyl allylation. In the carbonyl allylation by 1-chlorobut-2-ene with any tin(II) halide, the addition of tetrabutylammonium iodide (TBAI) accelerates the reaction and enhances gamma-syn selectivity. The use of tin(II) iodide and TBAI produces 2-methyl-1-phenylbut-3-en-1-ol with high yield and high syn-diastereoselectivity. The syn-diastereoselective carbonyl allylation of 1-chlorobut-2-ene using tin(II) iodide, a catalytic amount of TBAI, and NaI in DMI-H(2)O is applied to various aldehydes.     

New Heck-type reaction applied to the synthesis of protoporphyrin-IX derivatives

[reaction: se text] A new Heck-type reaction under catalysis by Pd for obtaining polysubstituted arylvinylydene derivatives of porphyrin systems is reported. The coupling between the Zn(II)-protoporphyrin-IX dimethylester Zn-2 and several bromo-aryl and iodo-aryl compounds in the presence of a new Pd catalyst has been studied. This coupling reaction, although providing moderate regioselectivity, gives quantitative conversion.