New highly efficient aziridine-functionalized tridentate sulfinyl catalysts for enantioselective diethylzinc addition to carbonyl compounds

New tridentate enantiomerically pure heteroorganic catalysts, containing hydroxyl, sulfinyl, and aziridine moieties, have proven to be highly efficient in the enantioselective diethylzinc addition to aryl and alkyl aldehydes to give the desired products in very high yields (up to 99%) and with ee’s up to 97%. The influence of the stereogenic centers located on the sulfinyl sulfur atom and in the aziridine moiety on the stereochemical course of the reaction are discussed.     

A highly efficient addition of allylic bromides to carbonyl compounds promoted by Cp2TiCl2(cat.)/Zn system

Aldehydes or ketones reacted with allylic bromides in the presence of Cp₂TiCl₂(cat.)/Zn system at room temperature to give homo-allylic alcohols in high yields.     

Lewis acid promoted highly stereoselective rearrangement of 2,3-aziridino alcohols: a new efficient approach to beta-amino carbonyl compounds

A new Lewis acid promoted rearrangement reaction of 2,3-aziridino alcohols was discovered, which involved the highly stereoselective construction of a diastereogenic quaternary carbon center and efficient formation of beta-amino carbonyl compounds in excellent yields. A wide variety of Lewis acids were proved to be effective for the reaction, and a possible reaction mechanism was also discussed.     

Eco-friendly polyethylene glycol promoted Michael addition reactions of α,β-unsaturated carbonyl compounds

Intra- and inter-nucleophilic addition reactions of different α,β-unsaturated carbonyl compounds were found to be highly effective without any additives in PEG-400 as a recyclable reaction medium under neutral conditions.     

The first ionic liquids promoted conjugate addition of azide ion to α,β-unsaturated carbonyl compounds

The first, highly efficient conjugate addition of azide ion to α,β-unsaturated carbonyl compounds promoted by the simple recyclable ionic liquids, bmimPF₆ and bmimBF₄, are described.     

A theoretical study of malononitrile addition to carbonyl compounds

The nucleophilic addition of the malononitrile anion (MN⁻) to formaldehyde was studied theoretically by the AM1 semiempirical MO method. The addition is found to be endothermic with a late productlike transition state on the reaction coordinate. Additions of MN⁻ to a series of carbonyl compounds were studied in order to investigate the substituent effect on the energetics of the title addition and the nucleophilic attack reactivity. The solvent effect was stimulated by hydrogen bonding a single molecule of water to the formaldehyde oxygen and/or to the MN⁻ anion. Its influence on the energetics and the transition-state geometry was estimated. The Hammond postulate was satisfied for the studied additions. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62 : 419–426, 1997     

Preparation of silyl substituted crotylzinc reagents and their highly diastereoselective addition to carbonyl compounds

Readily prepared beta-silyl substituted crotylzinc reagents undergo highly selective allylation of carbonyl compounds leading to syn-homoallylic alcohols.     

A highly efficient procedure for the oxathioacetalization of carbonyl compounds under solvent-free conditions

The novel efficient procedure has been developed for the oxathioacetalization of carbonyl compounds and 2-mercaptoethanol using the novel carbon-based sulfonic acid as catalyst under solvent-free condition at room temperature. The results showed that the novel catalyst was very efficient for the reactions with good to excellent yields in short time. The novel catalyst owned many advantages such as operational simplicity, without need of any solvent, small amount of usage, low cost of the catalyst used, high yields, applicability to large-scale reactions, reusability and chemoselectivity over the traditional catalysts, which made the catalyst one of the best choices for the reactions.     

A highly efficient large-scale asymmetric Michael addition of isobutyraldehyde to maleimides promoted by a novel multifunctional thiourea

A novel class of chiral multifunctional thioureas bearing a chiral lipophilic beyerane scaffold and a primary amino group were designed and prepared. The thioureas were proven to be effective for catalyzing the asymmetric Michael addition between isobutyraldehyde and maleimides with only 0.5 mol % catalyst loading, and exhibited double asymmetric induction. Both of the catalysts afforded the corresponding adduct with high to excellent yields (up to 98%) and excellent enantioselectivities (up to 99%). Furthermore, this catalytic system can be used efficiently in large-scale reactions with the yields and enantioselectivities being maintained at the same level.     

Copper(II) tetrafluoroborate as a novel and highly efficient catalyst for Michael addition of mercaptans to α,β-unsaturated carbonyl compounds

Copper(II) tetrafluoroborate has been found to be a new and highly efficient catalyst for Michael addition of thiols to α,β-unsaturated carbonyl compounds under solvent-free conditions and in H₂O at room temperature. The reactions are very fast and are completed in 2 min to 1 h affording high yields. The rate of thiol addition was dependent on the steric hindrance at the β-carbon of the α,β-unsaturated carbonyl substrate. In the case of chalcones, the reactions are best carried out in MeOH as solvent.     

The addition of carbonyl compounds to tetramesitylgermasilene and dimesitylgermylene

Hexamesitylsiladigermirane, 1 , has been photolyzed/thermolyzed in the presence of three representative carbonyl compounds: acetone, pivalaldehyde, and benzaldehyde. In each case, a [2 + 2] adduct between the carbonyl compound and Mes₂Ge = SiMes₂ was formed regioselectively to give a 2,3-silagermaoxetane. The 2,3-silagermaoxetanes have been fully characterized by IR and NMR (¹H, ¹³C, and ²⁹Si) spectroscopy and mass spectrometry. In two cases, the structures have been confirmed by X-ray crystallography: 4,4-dimethyl-2,2,3,3-tetramesityl-2,3-silagermaoxetane, 2a ; crystals are triclinic, space group P1 with Z = 2 in a unit cell of dimensions a = 12.318(3) Å, b = 12.436(2) Å, c = 11.884(2) Å, α = 100.13(1)°, β = 103.80(2)°, and γ = 89.97(2)°. The structure was solved by direct methods and refined by least squares on the basis of 2955 observed reflections to R₁ and wR₂ values of 0.0600 and 0.1363, respectively. The structure of 4-tert-butyl-2,2,3,3-tetramesityl-2,3-silagermaoxetane, 2b , was also determined; crystals are monoclinic, space group Cc with Z = 4 in a unit cell of dimensions a = 11.306(2) Å, b = 21.292(4) Å, c = 16.524(2) Å, and β = 106.83(1)°. The structure was determined by direct methods and refined by full-matrix least squares on the basis of 1817 observed reflections to R₁ and wR₂ values of 0.0621 and 0.1681, respectively. An adduct between dimesitylgermylene and the carbonyl compound was also isolated in each reaction. The structure of the adduct appears to depend upon the steric bulk of the group attached to the carbonyl carbon.     

A computational study on addition of Grignard reagents to carbonyl compounds

The mechanism of stereoselective addition of Grignard reagents to carbonyl compounds has been investigated using B3LYP density functional theory calculations. The study of the reaction of methylmagnesium chloride and formaldehyde in dimethyl ether revealed a new reaction path involving carbonyl compound coordination to magnesium atoms in a dimeric Grignard reagent. The structure of the transition state for the addition step shows that an interaction between a vicinal-magnesium bonding alkyl group and C=O causes the C-C bond formation. The simplified mechanism shown by this model is in accord with the aggregation nature of Grignard reagents and their high reactivities toward carbonyl compounds. Concerted and four-centered formation of strong O-Mg and C-C bonds was suggested as a polar mechanism. When the alkyl group is bulky, C-C bond formation is blocked and the Mg-O bond formation takes precedence. A diradical is formed with the odd spins localized on the alkyl group and carbonyl moiety. Diradical formation and its recombination were suggested to be a single electron transfer (SET) process. The criteria for the concerted polar and stepwise SET processes were discussed in terms of precursor geometries and relative energies.     

Amine-catalyzed addition of azide ion to alpha,beta-unsaturated carbonyl compounds

[formula: see text] A new protocol for the beta-azidation of alpha,beta-unsaturated carbonyl compounds is described. The method employs tertiary amines as catalysts for azide addition. The azide source is a 1:1 mixture of TMSN3 and AcOH. Tertiary amines, either in solution or bound to a solid support, are efficient catalysts for the reaction.     

Mesoporous aluminosilicate promoted protection and deprotection of carbonyl compounds

Mesoporous aluminosilicates are efficient heterogeneous catalysts for both the formation and hydrolysis of a range of acetals under mild conditions and in short reaction times.     

Palladium-catalyzed conjugate addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds and nitroalkenes

The addition of aryltrialkoxysilanes to alpha,beta-unsaturated carbonyl compounds (ketones, aldehydes) and nitroalkenes in the presence of SbCl(3), TBAF, AcOH, and a catalytic amount of Pd(OAc)(2), in CH(3)CN at 60 degrees C, provides the corresponding conjugate addition products in moderate to good yields. The addition of equimolar amounts of SbCl(3) and TBAF is necessary for this reaction to proceed smoothly. The arylpalladium complex, which is generated by the transmetalation from a putative hypercoordinate silicon compound, is considered to be the catalytically active species.