Shizuyoshi Sakai

Samarium(II) di-iodide induced reductive coupling of α,β-unsaturated esters with carbonyl compounds leading to a facile synthesis of γ-lactone

Samarium(II) di-iodide, which is a strong one-electron transfer reducing agent, is effective for the reductive coupling of α,β-unsaturated esters with carbonyl compounds, whereby substituted γ-lactones can easily be prepared in good to excellent yields under very mild conditions. Two mole equiv. of samarium(II) di-iodide to each mole equiv. of starting substrate always give reasonable yields. The presence of an alcohol is essential in the reaction, complex unidentified products being formed in the absence of an alcohol; t-butyl alcohol gave more satisfactory results than methanol and ethanol. The alcohol acts as a proton donor, the use of MeOD leading to a deuteriated γ-lactone. The reaction is applicable to both aliphatic and aromatic ketones or aldehydes, whereas the electrochemical method is limited to aliphatic substrates. The diastereoselectivity is examined in the reaction of 4-t-butylcyclohexanone with ethyl acrylate; an anti-isomer is produced predominantly (syn :anti= 1 : 9) as the result of selective axial attack. The reaction may proceed by a radical mechanism, and reaction may not involve a samarium ester homoenolate. The reaction is extended to the intramolecular reaction of an α,β-unsaturated keto ester (8-oxonon-2-enoate) leading to the ready synthesis of a bicyclic γ-lactone.

Preparation and electrochemical properties of palladium(0) complexes coordinated by quinones and 1,5-cyclooctadiene

The complexes Pd(quinone)(COD) (COD = 1,5-cyclooctadiene) are prepared by a ligand substitution reaction of Pd2(DBA)3 (DBA = dibenzylideneacetone) in the presence of both quinone and COD. Palladium(0) complexes coordinated by quinones only are formed in the reaction in the absence of COD. The cyclic voltammetric behavior of Pd(quinone)(COD) has been studied. The reduction potentials for quinones shifted toward negative values on coordination to palladium(0). The oxidation potentials for the central palladium(0) in Pd(quinone)(COD) depend on the electron-withdrawing ability of the free quinones, and are in the following series: quinone = p-benzoquinone < 5,8-dihydro-1,4-naphthoquinone ∼ 1,4-naphthoquinone < duroquinone. The shift of oxidation potentials for Pd(quinone)(COD) on changing the quinones as ligands is in contrast to that of Pd(quinone)(triphenylphosphine)2.

Insertion reactions of conjugated dienes with π-allylic palladium complexes

Abstract π-Allylic palladium complexes reacted with conjugated dienes to give diene-inserted products. Isoprene gave l,l-disubstituted allyl complexes rather than 1,2-disubstituted ones. Two types of allylic complexes were studied, and halogen-bridged dimer complexes showed lower reactivity than acetylacetonato complexes. When the allylic group or diene was varied, the reactivity decreased in the order: allyl > 2-methylallyl > 1-methylallyl > cinnamyl and butadiene > isoprene > chloroprene > 2,3-dimethylbutadiene The crotyl complex reacted with butadiene less readily, to give mainly the product with the structure: The reactivity variations and the reaction mechanisms are discussed.

Insertion reactions of diethylaluminium derivatives III. Reactions of diethylaluminium dimethylamide, ethanethiolate and ethanolate with lactones or acid anyhydrides

Abstract Diethylaluminium derivatives, Et 2 AIX (X=NME 2 or OEt) were found to react with β-propiolactone by Al bond cleavage of the Et 2 AIX and acyloxygen bond fission of the lactone to give selectively the corresponding diethylaluminium (2-aminocarbonyl) ethanolate or (2-alkoxycarbonyl)ethanolate Et 2 AlOCH 2 CH 2 COX. In the case of Et 2 AlSEt, the products were the mixture of Et 2 AlOCH 2 CH 2 COSEt and EtSCH 2 CH 2 COOAlEt 2 . The reactions of Et 2 AlNME 2 with γ-butyrolactone or phthalide occured with acyloxygen bond fission.

1,2-Regioselective reduction of α,β-unsaturated carbonyl compounds with lithium aluminium hydride in the presence of lanthanoid salts

An α,β-unsaturated carbonyl compound when reduced by lithium aluminium hydride in the presence of lanthanoid chloride, bromide, iodide, or acetylacetonate gives, selectivity, an allylic alcohol, while in its absence saturated alcohol formation predominates. Such reactions can be applied to various α,β-unsaturated carbonyl compounds such as aldehydes, ketones, esters, and lactones. In addition to its wide applicability, this reagent appears to be easier to use, than other known reducing reagents.

Intramolecular reductive cyclization of unsaturated keto- or aldo-esters by samarium(II) di-iodide: a ready synthesis of bicyclic γ-lactones

Treatment of unsaturated keto- or aldo-esters with Sml2 in tetrahydrofuran (THF) or THF–hexamethylphosphoramide affords bicyclic γ-lactones in moderate to good yields.

The formation of CPd σ complexes from the reaction between palladium(II) chloride and allylic sulphides

Abstract Allylic sulphides were found to react with palladium chloride in methanol in the presence of sodium carbonate at low temperature to give di-μ-chloro-bis(3-alkylor phenylmercapto-2-methoxypropyl)dipalladium(II). However, crotyl or cinnamyl sulphide did not give analogous complexes. Allylic sulphoxides were found to react with palladium chloride, but, from ethyl allyl sulphoxide alone the similar σ-complex was obtained in low yield. Benzyl phenyl sulphide gave exclusively bis(benzyl phenyl sulphide)dichloropalladium.

Insertion reactions of diethylaluminium derivatives: I. Reaction of diethylaluminium ethanethiolate and diethylaluminium dimethylamide with isocyanates or isothiocyanates

Diethylaluminium ethanethiolate and dimethylamide, Et2AlX (X = SEt and NMe2), were found to react with equimolar amounts of isocyanate or isothiocyanate, RNCY (R = Me, Ph, tert-Bu, cyclohexyl; Y = O and S). The occurrence of AlS or AlN bond cleavage was confirmed by elemental analysis and by infrared and proton magnetic resonance spectra of the 11 adduct obtained. Infrared spectra and cryoscopic molecular weight determinations suggested the existence of an equilibrium between the monomer and a dimer formed through the bridging of heteroatoms by aluminium. Hydrolysis of the adducts gave the corresponding S-ethyl thiocarbamate and substituted urea or thiourea derivatives. Formation as by-products of allophanate derivatives and cyclic trimers of the isocyanate indicated the occurrence of successive insertion reactions.

Insertion reactions of diethylaluminium derivatives II. reaction of diethylaluminium dimethylamide and diethylaluminium ethanethiolate with nitriles

Abstract Diethylaluminium dimethylamide, Et2AlNMe2, has been found to react with equimolar amount of benzonitrile or p-substituted benzonitriles, XC6H4CN (X = NO2, Me, OMe, NMe2), to give diethylaluminium benzamidine derivatives, Et2Al-N=C(XC6H4)-NMe2. These products result from addition of the Al-N bond across the CN bond. The order of reactivity for p-substituted benzonitriles is X = NO2τ H⋍CH3τOMe τ NMe2, the reverse of the order of π-electron density on CN group, which suggests the initial step of the reaction is not the formation of a π-complex, but the formation of the complex, RCN→Al(NMe2)Et2, which is followed by nucleophilic migration of the NMe2 group to the C atom of the CN group. Acetonitrile and benzyl cyanide react similarly with Et2AlNMe2 to give crystalline addition products. Ethyl Cyanoacetate reacts with evolution of an equivalent amount of ethane and formation of a solid. Diethylaluminium ethanethiolate, Et2AlSet, which reacts readily with isocyanates, reacts also with many nitriles, but the usual addition products are difficult to isolate except in the case of acetonitrile.

Reaction of α-halogeno ketones with carbonyl compounds promoted by CeI3, CeCl3–NaI, or CeCl3–SnCl2

Reaction of α-halogeno ketones with aldehydes in the presence of CeI3 in tetrahydrofuran is found to give α,β-unsaturated ketones in excellent yields under mild conditions. In contrast, treatment of α-halogeno ketones and carbonyl compounds with CeCl3–NaI or CeCl3–SnCl2 affords β-hydroxy ketones in good yields. It is assumed that these reactions proceed via cerium enolates. The combined reagents, however, cannot be applied to a Reformatsky-type reaction. Regiospecific and aldehyde chemoselective aldol synthesis are also described.