R. Noyori

Homogeneous catalysis in the decomposition of diazo compounds by copper chelates : Asymmetric carbenoid reactions

Abstract Bis9acetylacetonato)copper(II) catalyzes thermal decomposition of diphenyldiazomethane in benzene to afford tetraphenylethylene and benzophenone azine. The absence of 1,1,2,2-tetraphenylethane among the products is explained by assuming a copper carbenoid in which the carbene moiety is attached to the central copper atom as the fifth ligand. The apparently electrophilic nature of this carbenoid is illustrated by isolating cyclopropylamines upon reaction with enamines. Chemical evidence for the postulated coordination has been obtained by observing several instances of asymmetric synthesis, which proceed under influence of a chiral copper chelate, bis[N-( R )-α-phenethylsalicylaldiminato]copper(II), and its enantiomer. Following products have been obtained in partially resolved form from reactions of methyl or ethyl diazoacetate and diazomethane with appropriate optically inactive substrates: ethyl cis - and trans -2-phenylcyclopropanecarboxylate, methyl cis - and trans -3-phenyltetrahydrofuran-2-carboxylate, trans -1-methyl-2-phenylcyclopropane, trans -bicyclo[10.1.0]- cis -4, trans -8-tridecadiene and trans -bicyclo[10.1.0]-tridecane. Intramolecular cyclization of allyl diazoacetate and of 1-diazo-6-phenyl- trans -5-hexene-2-one occurs smoothly in the presence of the same copper chelate to afford 3-oxabicyclo[3.1.0]-hexan-2-one and 6-phenylbicyclo[3.1.0]hexan-2-one both in partially resolved state. The mechanism of these carbenoid reactions is discussed on the basis of further additional observations.

Asymmetric syntheses by means of (−)-sparteine modified organometallic reagents

Abstract Asymmetric induction has been observed in the reactions of organo-lithium and magnesium compounds complexed with a chiral tertiary diamine, (−)-sparteine. Debromination of gem -dibiomocyclopropanes with such complexed n-BuLi gives optically active allenic hydrocarbons, and this shows that the intermediate leading to allene is lithium carbenoid (or α-bromocyclopropyllithium) rather than free cyclopropylidene. Addition of organolithium or a Grignard reagent to carbonyl compounds proceeds dissymmetrically to afford carbinols of up to 22% optical purity. Finally lithiation of ethylbenzene with n-BuLi has been examined in the presence of (-⊃-sparteine and the resulting α-phenethyllithium complex yields optically active products.

Photochemical rearrangement of arenesulphonanilides to p-aminodiarylsulphones

Abstract Irradiation of arenesulphonanilides in an alcoholic solution induced the Fries-type rearrangement yielding p -amino-substituted diarylsulphones and arylamines. The absence of crossed rearrangement was observed upon photolysis of an equimolar mixture of p -toluenesulphonanilide and o -benzenesulphonotoluidide.

Photochemical reactions of trans-anethole

Abstract A novel dimer of trans-anethole has been obtained photochemically. The dimerization proceeds with strict stereospecificity and the structure of the dimer has been ascertained as 1,cis-2-di-p-anisyl-trans-3,trans-4-dimethylcyclobutane. The dimer was transformed into the corresponding diphenol, diacetate and 1,cis-2-dimethyl-trans-3,trans-4-diphenylcyclobutane. The hydrocarbon was independently obtained from β-truxinic acid by reduction. Some dimethyldiphenylcyclobutane isomers have been prepared analogously from cinnamic acid dimers and the NMR spectra have been compared. Anethole reacts photochemically with benzaldehyde and benzophenone to afford the corresponding oxetanes, some of which decompose spontaneously into stilbenes and acetaldehyde. The anethole dimer was not obtained in the presence of such carbonyl compounds, while isomerization to cis-anethole proceeds smoothly. Salicylaldehyde gives another type of 1:1-adduct, which has been shown to be 4-p-anisyl-2-hydroxy-3-methylchroman. An analogous hemiacetal was obtained by the reaction of salicylaldehyde and 1,1-diphenylethylene. Mechanistic implications of anethole photochemistry have been discussed.

Reaction of carbethoxycarbene with 2-phenyloxirane and 2-phenyloxetane

Abstract Thermal or photochemical decomposition of ethyl diazoacetate in 2-phenyloxirane gave a complex mixture, the analysis of which indicated that the reaction of carbethoxycarbene had proceeded according to the scheme summarized in Fig. 1. The reaction probably involves intermediate formation of an oxygen-ylide (IV), thus accounting for the observed oxygen-transfer and oxetane formation. Copper-catalysed thermal decomposition resulted in a more selective distribution of products, secondary reactions as well as the tar-formation being drastically reduced. The action of other carbenes such as dihalo-, phenyl- and diphenyl-carbene yielded less or no oxygen-transfer products and the formation of oxetane was not observed. In some cases, especially in the reaction of bis(benzene-sulphonyl)carbene, the major product was cyclic dimers of 2-phenyloxirane. 2-Phenyloxetane reacts more selectively with carbethoxycarbene to produce a mixture of cis and trans isomers of 2-carbethoxy-3-phenyltetrahydrofuran in 72–80% yield.

Preparation and photochemical isomerization of 2-cyclododecenones

Abstract Treatment of trans- or cis-epoxycyclododecane (I and II) with n-butyllithium yields the same product, trans-2-cyclododecenol (III). Oxidation of III with chromic acid affords a 4:1 mixture of trans- and cis-2-cyclododecenones (IV and V) the isomers being separated chromatographically. The cis enone V is thermodynamically less stable and is isomerized spontaneously at room temp to the trans enone IV. Irradiation of a cyclohexane solution of IV with a high-pressure mercury lamp gives V and a β,γ-unsaturated ketone, cis-3-cyclododecenone (VII). This cis enone VII is thermally and photochemically stable.

Reaction of phenylcarbene formed from benzaldehyde tosylhydrazone in certain solvents

Abstract Treatment of benzaldehyde tosylhydrazone (I) with sodium methoxide in various solvents under irradiation and/or heating yields products arising from phenylcarbene (IV) which is produced by photolytic or pyrolytic decomposition of initially formed phenyldiazomethane (III). Reaction products originating solely from the tosylhydrazone (I) are (VI ∼ XI) while those produced by the interaction with solvents are formulated as addition products of (VI) to olefinic and aromatic CC bonds and insertion products of (IV) to aliphatic and to aromatic CH bonds. The reaction with aniline yields an insertion product of (IV) to the NH bond, or N-benzylaniline, in 26% yield, besides ring-benzylated compounds. o -Toluadehyde and 2,4,6-trimethylbenzaldehyde tosylhydrazones react similarly.

Photochemical reaction of ethyl azidoformate with cyclic ethers and acetals

Abstract Irradiation of ethyl azidoformate dissolved in cyclic ethers (IIIA-VA) and acetals (VIA-VIIIA) yields insertion products (IIIB-VIIIB) of carboethoxynitrenes (IIS and IIT). The attack of the nitrenes occurs exclusively at the CH bond adjacent to the ether oxygen or adjoining acetal oxygens to produce a single insertion product in each case. Byproducts are urethane (IX) and the dimerization product (X) of amino radicals (XI). The effects of acetophenone as a sensitizer and of methylene chloride as a diluent have been examined and discussed. Reduction of IIIB and IVB with LAH produces 4-methylaminobutan-1-ol and 5-methylaminopentan-1-ol in 62 and 83% yields, respectively.

Reduction of gem-dibromocyclopropanes with chromium(II) sulphate

Abstract gem-Dibromocyclopropanes I are easily attacked by chromium (II) sulphate to produce allenes (V), monobromocyclopropanes (VI) and completely reduced cyclopropanes (VII) by the scheme formulated. The product distribution (Table 1) depends on the size of the second rings fused to the cyclopropane ring. Both cyclopropyl bromides isolated (VIa and VIb) have cis-configuration. As shown in Table 2 certain monobromocyclopropanes (cis-VIa and trans-VIb) are hydrolysed under such reduction conditions to give the respective allylic alcohols VIIIa and VIIIb, but no completely reduced products VII are produced.

The photochemistry of 1,2,3-triphenylaziridine

Abstract Photochemical behaviour of 1,2,3-triphenylaziridine has been investigated. Irradiation in alcoholic solvents induces a novel type of alcoholytic cleavage of the aziridine ring to give benzaldehyde acetals and N-benzylaniline. Competitively, fragmentation occurs to give rise to benzalaniline and phenylcarbene, the latter being trapped with alcohols as alkyl benzyl ethers. Photolysis in cyclohexene affords a 1,3-cycloaddition product, 1,2,3-triphenyloctahydroisoindole as a mixture of two stereoisomers.