One-pot synthesis of optically active allyl esters via lipase-vanadium combo catalysis

The combination of vanadium-oxo compounds (3 or 4) with a lipase produced the regio- and enantioconvergent transformation of racemic allyl alcohols (1 or 2) into optically active allyl esters. In this system, the vanadium compounds catalyzed the continuous racemization of the alcohols along with the transposition of the hydroxyl group, while the lipase effected the chemo- and enantioselective esterification to achieve the dynamic kinetic resolution.     

Asymmetric ene reaction catalyzed by chiral organoaluminum reagent

The asymmetric ene reaction of prochiral aldehydes with alkenes has been effected by chiral organoaluminum reagent providing optically active homoallylic alcohols in both enantiomeric forms with high enantiomeric purity.     

Selective Reactions Using Organoaluminum Reagents [New Synthetic Methods (54)]

In addition to their high oxyphilicity, organoaluminum compounds are endowed with ambiphilic character. These properties can be successfully utilized in developing new synthetic reactions with unique selectivities. Especially noteworthy are the organoaluminum-promoted Beckmann rearrangement of oxime sulfonates, new syntheses of polyamino macrocycles via reductive cleavage of aminals and amidines by diisobutylaluminum hydride, the diastereoselective cleavage of chiral acetals by organoaluminum compounds leading to optically active secondary alcohols, allylic alcohols, and β-substituted carbonyl compounds, and biomimetic terpene syntheses. These and other examples, which illustrate the characteristics of organoaluminum chemistry, are used to demonstrate the distinct advantages of organoaluminum reagents in selective organic synthesis.     

结构新颖的金属双核烯丙基试剂的合成及其芳香醛烯丙基化反应

报道了一个简捷的芳香醛的烯丙基化反应的新体系. 通过使用新型的金属双核烯丙基锡试剂(含有Sn—M键, M=Mn或Fe)与醛在二氯甲烷中反应, 无需使用任何辅助试剂, 直接得到较高产率(42％~98％)的高烯丙基醇. 实验结果证明过渡金属基团及M—Sn键具有相当高的活化锡原子上的烯丙基基团的作用.     

Transition metal promoted alkylations of unsaturated alcohols: the methylation and ethylation of 3-buten-1-ol using titanium tetrachloride-organoaluminum systems

The ethylation and methylation of the olefinic linkage in 3-buten 1-ol by incorporating the alkenol into a titanium-organoaluminum system was studied under a variety of conditions. Systems were derived from titanium tetrachloride and the organoaluminum compounds Al(C₂H₅)₃, Al(C₂H₅)₂Cl, Al(CH₃)₃, and Al(CH₃)₂Cl. With diethylaluminum chloride the major products obtained were 1-hexanol, 3-methyl-1-pentanol, trans-3-hexen-1-ol, and 1-butan I. Triethylaluminum gave no alkylation products. Dimethylaluminum chloride and trimethylaluminum gave product distributions similar to the analogous diethylaluminum chloride system.     

Snytheses and Reactions of O,N,N′-Trisubstituted Isoureas

The CuCl₂-catalysed addition of alcohols to aliphatic caribodiimides (particularly diisopropylcarbodiimide) to form O,N,N′-trialkylisoureas may, in the case of bifunctional hydroxy compounds (esters of α-hydroxycarboxylic acids, diols, halogeno alcohols, amino alcohols, and cyclic hydroxy ethers), continue to give 5-, 6-, and 7-membered 1,3-O,N or 1,3-N,N heterocycles. O,N,N′-Trialkylisoureas are selective alkylating agents. Thus alcohols with allyl structures can be etherified with diisopropylcarbodiimide; a new method of esterification via O,N,N′-trialkylisoureas has been applied to mesitylenecarboxylic acid.     

Synthesis and polymerization of allyloxyacetaldehyde

Allyloxyacetaldehyde (AOA) was synthesized by the Williamson reaction between sodium allyl alcoholate and bromoacetaldehyde dimethyl acetal. Highly reactive crystalline poly(allyloxymethyl)oxymethylene was obtained from AOA by using organoaluminum compounds as initiators at low temperature. The influence of initiators, solvents, and temperature on the polymerization was examined. Conspicuous exothermal behavior of the resulting polymer observed in the temperature range of 110–140°C in air with a differential scanning calorimeter, was not only due to an oxidative scission of the polyoxymethylene chain but also due to a chain reaction of neighboring allyl side groups in the polymer chain.     

Organoaluminum chemistry and its application to the initiation of carbenium ion polymerization

Organoaluminum compounds are weak Lewis acids, which specifically react with a number of reagents (or bases) and generate an electrophile (initiator)gegenion pair, reminiscent of classical Friedel—Crafts complexes. These complexes, under suitable reaction conditions, initiate polymerization of cationically polymerizable monomers producing useful high molecular weight polymers. In recent years a number of such organoaluminum-initiator systems have been systematically explored and their chemistry unravelled. As a consequence new insights have been gained which has led to newer applications of organoaluminum compounds in organic as well as new polymer synthesis.The present paper briefly summarizes the results in this area, especially from the point of view of initiator generation. Some recent results on the initiation of carbenium ion polymerizations using the oxyhalides of sulfur and phosphorous in conjunction with organoaluminum compounds are discussed.     

Use of oxo-metallic derivatives in isomerisation: Reactions of unsaturated alcohols

The isomerisation of α-acetylenic alcohols to ethylenic carbonyl derivatives and the isomerisation of α-ethylenic alcohols to the corresponding allyl alcohols may be effected in good yields in a single step using oxometallic derivatives. The vanadate esters are particularly efficient. Mechanistic explanations are given.     

Nucleophilic and organometallic displacement reactions of allylic compounds: stereo-and regiochemistry

Allylic alcohols, esters, halides and related compounds have been of mechanistic and synthetic interest for years. This Report focuses on the stereo- and regiochemical aspects of three reaction types: the S_N2' reaction (bimolecular nucleophilic substitution with allylic rearrangement); displacement reactions effected by organometallic reagents; the conversion of allylic alcohols into halides.     

BiCl3-catalyzed propargylic substitution reaction of propargylic alcohols with C-, O-, S- and N-centered nucleophiles

A general and efficient BiCl3-catalyzed substitution reaction of propargylic alcohols with carbon and heteroatom-centered nucleophiles such as allyl trimethylsilane, alcohols, aromatic compounds, thiols and amides, leading to the construction of C-C, C-O, C-S and C-N bonds, has been developed.     

A general and efficient FeCl3-catalyzed nucleophilic substitution of propargylic alcohols

A general and efficient FeCl3-catalyzed substitution reaction of propargylic alcohols with carbon- and heteroatom-centered nucleophiles such as allyl trimethylsilane, alcohols, aromatic compounds, thiols, and amides, leading to the construction of C-C, C-O, C-S and C-N bonds, has been developed.     

Allylation of Carbonyl Compounds Mediated by Aluminum/Fluoride Salts in Water

A novel mediator (Al/KF) has been developed and employed in the Barbier‐type alkylations of various aldehydes and ketones with alkyl halide in water. The carbonyl compounds could be effectively converted into corresponding homoallylic alcohol in good yields only when allyl bromides or substituted allyl bromides were used as halides. Aromatic aldehydes could afford homoallylic alcohols in high yields, unfortunately, the allylation of aromatic aldehyde substituted by nitro‐ or amino‐group could not proceed smoothly, and the allylation yields of ketones and aliphatic carbonyl compounds were lower under the same condition. The diastereoselectivity and regioseletivity of the reaction have also been studied, the predominant products preferred the erythro‐ or anti‐isomer in dominant γ‐adduct by using Al/KF mediated allylation of benzaldehydes with cinnamyl bromide and ethyl 4‐bromo‐2‐butenoate in water.     

Recent advances in the activation of boron and silicon reagents for stereocontrolled allylation reactions

Despite the popularity of boron and silicon allylation reagents in stereocontrolled synthesis, they suffer from a number of inherent limitations that have slowed down their development as synthetic tools for nucleophilic additions to carbonyl compounds and imine derivatives. These limitations are the low reactivity and diastereoselectivity of allyl trialkylsilane reagents, and the lack of catalytic systems for the activation and substoichiometric control of enantioselectivity in the additions of allyl boron reagents. To develop more efficient and general methods for the control of absolute stereochemistry in the resulting homoallylic alcohols, new approaches aimed at solving the problem of activation of allylic boron and silicon reagents are needed. This Minireview describes a number of recent approaches that have been devised to address this problem.     

TBAF‐Mediated Dimerization Reaction of β,γ‐Unsaturated Arylketones

A simple and high‐yield method for the synthesis of several 1,5‐diaryl‐1,5‐dicarbonyl compounds has been established starting from TBAF‐mediated isomerization and dimerization reaction of β,γ‐unsaturated arylketones (allyl arylketones) with mono‐, di‐, and tri‐methoxy groups, which is derived from allylation of commercially available different benzaldehydes and followed by oxidation of the resulting secondary alcohols.     

(2,7-Disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) as bidentate organoaluminum Lewis acids: elucidation and synthetic Utility of the double electrophilic activation phenomenon

A series of (2,7-disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) (2) has been readily prepared in situ by treatment of the requisite 2,7-disubstituted-1,8-biphenylenediol (1) with Me3Al (2 equiv) in CH2Cl2 at room temperature; this primarily relies on the successful establishment of a new synthetic procedure of 1 starting from inexpensive m-anisidine. Evaluation of 2 as a bidentate organoaluminum Lewis acid has been performed by the reduction of ketonic substrates using Bu3SnH as a hydride source in comparison to the conventional monodentate Lewis acid dimethylaluminum 2,6-xylenoxide (11), uncovering the significantly high activation ability of 2 toward carbonyl. Particularly, (2,7-dimethyl-1,8-biphenylenedioxy)bis(dimethylaluminum) (2a) exerted the highest reactivity, which has also been emphasized in the Mukaiyama aldol reaction. The structure of the bidentate Lewis acid 2 was unambiguously determined by single-crystal X-ray diffraction analysis of 2g possessing a bulky 3,5-di-tert-butylphenyl substituent, revealing the rigid dimeric assembly in the solid state. The double electrophilic activation of carbonyl substrate by 2a has been supported by low-temperature 13C NMR analysis as well as theoretical study using the Gaussian 98 program. Moreover, unique stereoselectivity has been observed in the 2a-promoted Mukaiyama Michael addition, and highly chemoselective functionalization of carbonyl compounds in the presence of their acetal counterparts has been realized using 2a. Finally, the effectiveness of 2a for the activation of ether functionality has been demonstrated in the Claisen rearrangement of allyl vinyl ethers.     

A convenient procedure for bismuth-mediated Barbier-type allylation of aldehydes in water containing fluoride ions

A new and convenient procedure for synthesis of homoallylic alcohols in generally good to excellent yields has been developed. The bismuth-mediated Barbier-type allylation of aldehydes (aromatic, aliphatic, alicyclic and heterocyclic) with allyl bromide has been carried out smoothly in water in the presence of fluoride ions.     

Remote stereocontrol using functionalized allylmetal reagents

Alk-2-enyl(trialkyl)stannanes with heteroatom substituents at the 4-, 5-, and 6-positions are transmetallated stereoselectively using tin(IV) halides to generate allyltin trihalides, which react with aldehydes to give (3Z)-homoallylic alcohols with efficient 1,5-, 1,6-, and 1,7-stereocontrol. This chemistry has been used to develop new strategies for natural product synthesis. Because of the toxicity of organotin reagents and the problems in removing organotin residues from reaction products, alternative procedures that avoid the use of organotin reagents have been investigated. To date, alk-2-enylgermanium reagents have been shown to deliver effective 1,5- and 1,6-stereocontrol, which is analogous to that observed for the organotin compounds. Organobismuth intermediates, which can be generated from allyl bromides and zinc-bismuth(III)iodide, react with aldehydes with efficient 1,5-stereocontrol which is complementary to that observed with the organo-stannanes or -germanes in that (3E)-homoallylic alcohols are obtained.     

Highly diastereoselective hydrostannylation of allyl and homoallyl alcohols with dibutyl(trifluoromethanesulfoxy)stannane

Dibutyl(trifluoromethanesulfoxy)stannane (Bu2Sn(OTf)H, 1a) was found to be very valuable for highly diastereoselective homolytic hydrostannylation of allyl and homoallyl alcohols. alpha,beta-Disubstituted allyl alcohols and alpha,gamma-disubstituted homoallyl alcohols were converted into gamma- and delta-stannylated alcohols with high 1,2-syn and 1,3-syn diastereoselectivity, respectively. The origin of the stereochemical outcomes can be rationalized by conformational fixation of the intermediary beta-stannylalkyl radical by coordination of the hydroxy group to the Lewis acidic tin center.     

Organoboron compounds,synthesis of allyl(dialkyl)boranes and diallyl(alkyl)boranes

Highly reactive allyl(dialkyl)-, crotyl(dialkyl)-, 3,3-dimethylallyl(dialkyl)-(= prenyl(dialkyl), and diallyl(alkyl)-boranes were prepared by allylation of esters R₂BOR′, RB(OR′)₂ or thioesters R₂BSR′ (R = alkyl) using allylic derivatives of aluminium, magnesium or boron in exchange reactions.The titled compounds are stable up to 100°C and do not symmetrize even on heating at 100°C for a long time. PMR spectroscopy data show that the characteristic feature of these compounds is a permanent allyl rearrangement, the rate of which increases with an increase in temperature. For allyl(diethyl)-borane at 100°C and 125°C the rates are equal to 2500 and 5000 sec^?1 respectively; activation energy of the rearrangement amounts to 11.8±0.2 kcal mol^?1.The boronallyl bonds in unsymmetrical allyl(alkyl)boranes readily split under the action of water and alcohols, protonolysis being accompanied by allyl rearrangement, crotyl and prenyl compounds are converted into 1-butene or 3-methyl-1-butene, respectively.