An indium-TMSCl promoted reaction of diphenyl diselenide and diorganyl disulfides with aldehydes: novel routes to selenoacetals, thioacetals and alkyl phenyl selenides

The reactions of diphenyl diselenide and dialkyl disulfides with aldehydes in the presence of In-TMSCl have been investigated. Aliphatic aldehydes provide the corresponding selenoacetals and aromatic aldehydes lead predominantly to benzyl phenyl selenides on reaction with diphenyl diselenide. However, the reaction of dimethyl disulfide and diphenyl disulfide with both aromatic and aliphatic aldehydes produce dithioacetals. This provides a novel route to the synthesis of selenoacetals, thioacetals and selenides from aldehydes.     

Highly enantioselective phenylacetylene additions to both aliphatic and aromatic aldehydes

The readily available and inexpensive BINOL in combination with Ti(O(i)Pr)(4) is found to catalyze the reaction of an alkynylzinc reagent with various types of aldehydes including aliphatic aldehydes, aromatic aldehydes, and other alpha,beta-unsaturated aldehydes to generate chiral propargyl alcohols with 91-99% ee at room temperature. No previous chiral catalysts have exhibited such a broad scope of enantioselectivity with respect to the type of aldehydes for this reaction. [reaction: see text]     

Silica Phosphoric Acid: An Efficient and Recyclable Catalyst for the Solvent-Free Synthesis of Acylals and Their Deprotection in MeOH

Silica phosphoric acid was used as an efficient, mild, and recyclable solid catalyst for the synthesis of acylals from various structurally diverse aldehydes and acetic anhydride under solvent-free conditions. The acylation of aldehydes was highly chemoselective, and no ketone was acylated, which provided a method for the synthesis of acylals from aldehydes in the presence of ketones. Silica phosphoric acid–catalyzed deprotection of acylals to the corresponding aldehydes in MeOH has also been developed with excellent yield. The deprotection of the acylals of aromatic aldehydes took priority over those of aliphatic aldehydes.     

The oxidation of aldehydes to acids with calcium hypochlorite [Ca(OCl)2]

Calcium hypochlorite is an efficient reagent for the oxidation of aldehydes to the corresponding acids. Reactions are carried out at ambient temperature in aqueous acetonitrile-acetic acid solution. Aliphatic aldehydes and aromatic aldehydes with electron withdrawing groups afford good to excellent yields. Nuclear chlorination is the preferred reaction in aromatic aldehydes with electron donating groups.     

Radical mediated-direct conversion of aldehydes into acid bromides

A method of preparing acid bromides directly from aldehydes with Br₃CCO₂Et under radical conditions was developed. Aromatic aldehydes with electron-donating group were found to be more reactive than aromatic aldehydes with electron-withdrawing group and aliphatic aldehydes under reaction conditions.     

An indium-TMSCl promoted reaction of diphenyl diselenides and aldehydes: novel routes to selenoacetals and alkyl phenyl selenides

The reaction of diphenyl diselenides with aldehydes in the presence of In-TMSCl has been investigated. Aliphatic aldehydes provide the corresponding selenoacetals, whereas aromatic aldehydes lead predominantly to alkyl phenyl selenides under the same reaction conditions. This constitutes a new approach for the synthesis of selenoacetals and selenides from aldehydes.     

Aldehyde enolates III direct sulfenylation and iodination of aldehyde anions.

Directly generated potassium enolates of aldehydes react with diphenyldisulfide to give the α-sulfenylated aldehydes. Reaction with iodine likewise provides the α-iodo aldehydes.     

Stereochemistry of the allylation and crotylation reactions of alpha-methyl-beta-hydroxy aldehydes with allyl- and crotyltrifluorosilanes. Synthesis of anti,anti-dipropionate stereotriads and stereodivergent pathways for the reactions with 2,3-anti- and 2,3-syn-alpha-methyl-beta-hydroxy aldehydes

A new method for the stereoselective synthesis of the anti,anti-dipropionate stereotriad via the reaction of alpha-methyl-beta-hydroxy aldehydes with (Z)-crotyltrifluorosilane (24) is described. These reactions were designed to occur through bicyclic transition states (e.g., 31) in which the silane reagent is covalently bound to the beta-hydroxyl group of the aldehyde and the crotyl group is transferred intramolecularly. This methodology was used to synthesize the C(7)-C(16) segment (58) of zincophorin, which contains a synthetically challenging all-anti stereopentad unit. Surprisingly, 2,3-anti- and 2,3-syn-alpha-methyl-beta-hydroxy aldehydes react in a stereodivergent manner with 24: 2,3-anti-beta-hydroxy aldehydes give the targeted anti,anti-dipropionate adducts with high selectivity, but the reactions of 2,3-syn-beta-hydroxy aldehydes are poorly selective. The stereodivergent behavior of 2,3-syn- vs 2,3-anti-alpha-methyl-beta-hydroxy aldehydes is also exhibited in their reactions with the allyl- (68) and (E)-crotyltrifluorosilanes (27). Competition experiments performed with beta-hydroxy aldehydes 37a (anti) and the corresponding p-methoxybenzyl (PMB) ether 48, and between aldehyde 39 (syn) and the PMB ether 90, established that the 2,3-anti-beta-hydroxy aldehydes react predominantly through bicyclic transition states while the 2,3-syn aldehydes react predominantly through conventional Zimmerman-Traxler transition states. NMR studies established that both the 2,3-syn and the 2,3-anti aldehydes form stable, pentavalent silicate intermediates (98 and 100) with PhSiF(3), but chelated structures 99 and 101 could not be detected. The activation energies for the competing bicyclic and conventional Zimmerman-Traxler transition states were calculated by using semiemperical methods (MNDO/d). These calculations indicate that the stereodivergent behavior of the 2,3-syn-beta-hydroxy aldehydes and the 2,3-anti-beta-hydroxy aldehydes is due to differences in nonbonded interactions in the bicyclic transition states. Specifically, nonbonded interactions in the bicyclic transition states for the allylation/crotylation reactions of the 2,3-syn-beta-hydroxy aldehydes permits the traditional Zimmerman-Traxler transition states to be preferentially utilized.     

Etude des aldimines lithiees: II. Preparation d'aldehydes a groupement halogenovinylique. Application a la synthese d'oxo-3 cyclopentenes et d'aldehydes γ acetyleniques

The condensation of metallated aldimines, prepared from activated lithium dialkylamides, with different dihalogenoalkenes gives aldehydes with a halogenovinylic group. Acidic hydrolysis of these aldehydes leads directly to cyclopentenones. When treated with an excess of activated amide, halogenovinylic aldimines give γ-acetylenic aldehydes.     

Lewis base activation of lewis acids. Addition of silyl ketene acetals to aldehydes

The weak Lewis acid silicon tetrachloride can be activated by catalytic amounts of the chiral bisphosphoramide (R,R)-3 to form a highly reactive, chiral trichlorosilyl cation which is an extremely effective promoter of aldol addition reactions between aldehydes and silyl ketene acetals. The tert-butyldimethylsilyl ketene acetal of methyl acetate adds nearly instantaneously to aromatic and olefinic aldehydes as well as aliphatic aldehydes (albeit more slowly) with excellent enantioselectivity. The homologous tert-butyldimethylsilyl ketene acetal of tert-butyl propanoate adds with nearly exclusive anti diastereoselectivity to a similar range of aldehydes also with excellent enantioselectivity. The origin of the slower reaction rate with aliphatic aldehydes is revealed to be the formation of chlorosilyl ether adducts.     

Chemoselective Carbonyl Reduction Mediated By Low-Valent Titanium

Utilizing the rate difference in alkoxy alkyl radical formation from aldehydes versus ketones with low-valent titanium, aldehydes are preferentially reduced with tributyltin hydride. The difference in reactivity allows aldehydes to be reduced in the presence of ketones without laborious protection-deprotection steps.     

Reinvestigation of the grignard reactions with formic acid. A convenient method for preparation of aldehydes

Grignard reagents react with formic acid in tetrahydrofuran to produce aldehydes in relatively good yields Various aldehydes such as alkyl, aryl, allyl, benzyl and vinyl aldehydes were prepared from the corresponding Grignard reagents. The reaction with vinyl Grignard reagents proceeded with retention of configuration.     

Highly chemoselective and efficient Strecker reaction of aldehydes with TMSCN catalyzed by MgI2 etherate under solvent-free conditions

Abstract

Strecker reaction of various substituted aromatic aldehydes, heteroaromatic aldehydes, aliphatic aldehydes and α,β-unsaturated aldehydes with trimethylsilyl cyanide (TMSCN) was realized in the presence of 5?mol % of MgI₂ etherate in a mild, efficient and highly chemoselective manner under solvent-free conditions.     

叔膦参与下联烯酸酯与醛的反应

联烯酸酯是近年来研究较多的一类重要的缺电子联烯,具有丰富的化学反应.本文着重总结了近年来在叔膦参与下(催化或化学计量方式)联烯酸酯与醛的新反应,包括2,3-丁二烯酸酯与醛的成环反应、γ-取代联烯酸酯与醛的[3+2]环加成反应和烯化反应、α-取代联烯酸酯与醛的Vinylogous Wittig反应以及环丙烷化反应,并从反应机理的角度,探讨了联烯酸酯与亲电试剂活化烯、亚胺和醛在反应性上的差异.在这些重要的化学转化中,叔膦的特殊性质如亲核性与夺氧能力起了关键的作用.     

Direct catalytic asymmetric alpha-amination of aldehydes

The first direct catalytic asymmetric alpha-amination of aldehydes is described herein. alpha-Unbranched aldehydes react in this novel proline-catalyzed reaction with dialkyl azodicarboxylates to give alpha-amino aldehydes in excellent yields and enantioselectivities.     

The formation of novel 1,3-dioxolanes: atypical Baylis-Hillman reaction of a sesquiterpene lactone parthenin

The Baylis-Hillman reaction of a sesquiterpene lactone parthenin with various aldehydes gave unexpected products containing a 1,3-dioxolane moiety. Both small aliphatic and aromatic aldehydes produced 1,3-dioxolanes, whereas higher aliphatic aldehydes produced normal Baylis-Hillman products.     

Organocatalytic SOMO reactions of copper(I)-acetylide and alkylindium compounds with aldehydes

The derivatisation of aldehydes in their α-position is an important facet of organic synthesis. Organocatalytic radical reactions afford α-functionalised aldehydes via a SOMO activation pathway. New organo-SOMO reactions of aldehydes with copper(I)-acetylide and alkylindium reagents are detailed. These reactions proceed well under the catalysis of chiral imidazolidinones. The corresponding functionalised aldehydes were obtained with acceptable yields, but with only low enantiomeric ratios.     

Aldehyde separation by polymer-supported oligo(ethyleneimines)

Chlorosulfonated styrene (10%) divinylbenzene resin beads reacted with an excess of ethylenediamine (EDA), diethylenetriamine (DETA), and triethylenetetramine (TETA) to give the corresponding sulfonamides with pendant oligo(ethyleneimines). The resulting modified resins are useful in the separation of aldehydes from hydrocarbon mixtures. Sorption of aldehydes occurs through formation of both Schiff base and five-membered (imidazoline) rings. Sorbed aldehydes can readily be stripped from the resins by treating with dilute acid solutions. Since the sulfamide bond has a reasonable stability toward acid-base hydrolysis, the loaded resins can be regenerated and recycled by simple acid-base washings, without losing their activity. In the present study, sorption and desorption kinetics of acetaldehyde, benzaldehyde, and salicylaldehyde have been investigated under different conditions. The aldehyde sorption obeys second-order kinetics. The method presented is applicable for all aromatic aldehydes. However, in the case of aliphatic aldehydes carrying an α-hydrogen, aldol condensation products form in solution. So aliphatic aldehydes and their aldol products are sorbed together by the resins. This limits the recovery of aliphatic aldehydes. Consequently, the resins described are cost effective sorbents for the removal and recovery of aromatic aldehydes from various mixtures. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2857–2864, 1997     

Reaction of beta-ethoxyvinyl lithiums generated from phenyltellanyl- and ethyltellanylacetaldehyde diethyl acetals with aldehydes and ketones and successive hydrations

Reactions of alpha-tellanyl-beta-ethoxyvinyl lithiums of aldehydes and ketones proceeded in good to high yields and the successive treatment with acids gave the alpha-tellanyl alpha,beta-unsaturated aldehydes. alpha-Tellanyl alpha,beta-unsaturated aldehydes easily transformed to more useful compounds.     

Automated HPLC-HRGC: A powerful method for essential oil analysis. Part III. Aliphatic and terpene aldehydes of orange oil

The application of a new method, computer-controlled on-line HPLC-HRGC, to the analysis of the components of sweet orange oil has enabled the determination of aldehydes without interferences. HPLC was used to separate the oil aldehydes into three fractions, aliphatic aldehydes, sesquiterpene aldehydes, and monoterpene aldehydes. These fractions were transferred automatically to the GC, where the individual aldehydes were separated into well resolved chromatographic peaks.