Electron-deficient Aromatic Aldehydes Research Articles

Y(OTf)3-Salazin-Catalyzed Asymmetric Aldol Condensation.

The chiral aziridine-containing vicinal iminophenol tridentate ligands (named salazins) are a class of readily prepared chiral ligands from enantiopure aziridines and salicylaldehydes. Their scandium and yttrium triflate complexes show excellent reactivity and enantioselectivities in the catalytic asymmetric aldol condensation of electron-deficient aromatic aldehydes and ketones, including acetone and cycloalkanones. The stereoselectivity is rationalized to the strong π-stacking interaction between aromatic aldehydes and the vicinal iminophenol group in the chiral ligands.

Photocatalytic 1,4-Addition of Aromatic Aldehydes or Ketones via Umpoled Carbinol Anions

AbstractA 1,4-addition reaction of aromatic aldehydes or ketones to electron-deficient olefins was achieved under photocatalytic conditions. In the reaction, an umpoled carbinol anion generated in situ through two successive one-electron reductions of the carbonyl compound reacted nucleophilically with the electron-deficient olefin. Various electron-deficient aromatic aldehydes and ketones successfully underwent the reaction to afford the corresponding γ-functionalized alcohols.

Mild, Modular, and Convergent Synthesis of Helical Naphtho[2,1-c]chromenes via a Multistep Cyclization/Aromatization Cascade Sequence.

Tetracyclic 6H-naphtho[2,1-c]chromenes are expeditiously synthesized through a BF3·OEt2-mediated, three-step cascade reaction, creating new central pyran and aromatic rings. The cascade involves the addition of phenol-derived alkynyl substrates to BF3-activated aldehydes followed by alkyne-Prins cyclization, Friedel-Crafts reaction, and final elimination. Aliphatic and electron-deficient aromatic aldehydes afford the products in 50-74% isolated yields, but benzaldehyde and tolualdehyde resulted in lower yields. X-ray analysis of a p-bromophenyl derivative (5aA) shows the two aromatic moieties are twisted by 28° to create a helical backbone.

N-Methylpyrrolidone Hydroperoxide/Cs2 CO3 as an Excellent Reagent System for the Hydroxy-Directed Diastereoselective Epoxidation of Electron-Deficient Olefins.

This report introduces N-methylpyrrolidone hydroperoxide (NMPOOH)/base as an excellent reagent system for hydroxy-directed syn selective epoxidation of electron-deficient olefins, characterized by high diastereoselectivity, short reaction times and remarkable chemoselectivity, especially in presence of oxidatively labile nitrogen or sulfur atoms. NMPOOH also proves efficient in the oxidation of electron-deficient aromatic aldehydes, in the removal of oxazolidinone chiral auxiliary, and in the functionalization of alkenes and alkynes, showing wide application potential.

Michael-Type Adducts of 3-Carbethoxycoumarins via Diels-Alder Reaction: Tandem Ring Construction of Furopyranochroman-2-one Skeletons

Diels-Alder reaction of furan with electron-deficient 3-carbethoxycoumarins gave the Michael-type adducts obtained from the rearrangement of the intermediate Diels-Alder adducts, instead of the Diels-Alder cycloadducts. Trapping of the dipolar intermediate with electron-deficient aromatic aldehydes gave a one-pot access to fused furo[3,2-b]pyranochroman-2-ones with multiple stereogenic centers. Ring opening of the lactone moiety gave a facile route to generate diverse scaffolds.

Fluorinated 1-phenyl-1H-tetrazol-5-yl sulfone derivatives as general reagents for fluoroalkylidene synthesis.

Julia-Kocienski olefination reagents 1-fluoropropyl, (cyclopropyl)fluoromethyl, 1-fluoro-2-methyl-2-propenyl, and 1-fluoro-5-hexenyl 1-phenyl-1H-tetrazol-5-yl (PT) sulfones were prepared by metalation followed by electrophilic fluorination. Although metalation-fluorination of n-propyl, 5-hexenyl, and (cyclopropyl)methyl PT-sulfones proceeded under homogeneous conditions, fluorination of 2-methyl-2-propenyl PT-sulfone required heterogeneous fluorination conditions. Condensation reactions of fluoro PT-sulfones with aldehydes resulted in fluoroalkylidenes in high yields. Screening of olefination conditions showed that stereoselectivity depended on reagent and carbonyl structure and can in many cases be tuned either toward E- or Z-selectivity. For example, LHMDS-mediated condensations of 1-fluoropropyl PT-sulfone in the presence of MgBr(2) x OEt(2) were Z-selective with electron-rich aromatic aldehydes, a hindered aromatic aldehyde, and cinnamaldehyde. Low-temperature KHMDS-mediated condensations were E-selective with electron-rich and electron-deficient aromatic aldehydes and Z-selective with n-octanal. Dialkyl, aryl alkyl, and diaryl ketones reacted as well to give fluoro olefin products in 71-99% yields.

P(PhCH2NCH2CH2)3N: An Efficient Lewis Base Catalyst for the Synthesis of Propargylic Alcohols and Morita−Baylis−Hillman Adducts via Aldehyde Alkynylation

Proazaphosphatrane P(PhCH(2)NCH(2)CH(2))(3)N (1a) is an efficient catalyst for the addition of aryl trimethylsilyl alkynes to a variety of aromatic, aliphatic, and heterocyclic aldehydes in THF at room temperature. The reaction conditions are mild and employ a low catalyst loading (ca. 5 mol %). Only propargylic alcohols were isolated in good to excellent isolated yields when electron-rich, electron-neutral, heterocyclic, and aliphatic aldehydes were employed, whereas beta-branched Morita-Baylis-Hillman (MBH) type adducts were isolated with electron-deficient aromatic aldehydes after conventional acid hydrolysis of the TMS ether products. Alkynes containing heterocyclic and aromatic groups bearing electron-withdrawing or -donating substituents underwent clean addition to cyclohexanecarboxaldehyde and to electron-rich aromatic aldehydes to give propargylic alcohols in excellent isolated yields. beta-Branched Morita-Baylis-Hillman (MBH) type adducts were isolated when electron-deficient aromatic aldehydes were employed. Reaction pathways to both types of products are proposed.

A synthesis of di- and tri-substituted β,γ-unsaturated esters from aldehydes by the magnesium carbenoid 1,2-CH and 1,2-CC insertion as the key reaction

Addition reaction of 1-chlorovinyl p-tolyl sulfoxides, which were derived from aldehydes, with lithium enolate of tert-butyl acetate at −78 °C in THF gave adducts in high yields. Treatment of these adducts with Grignard reagents resulted in the formation of magnesium carbenoids via the sulfoxide–magnesium exchange reaction. When the adducts were derived from alkyl aldehydes or electron-deficient aromatic aldehydes, carbenoid 1,2-CH insertion reaction took place from the magnesium carbenoids to afford β,γ-unsaturated butyric esters having a substituent at the β-position. On the other hand, when the adducts were derived from electron-rich aromatic aldehydes, carbenoid 1,2-CC insertion reaction took place from the magnesium carbenoids to give β,γ-unsaturated butyric esters having the aromatic group at the γ-position. Highly stereospecific 1,2-CC insertion reactions were observed in the latter reactions. When the addition reactions were quenched with iodoalkanes, the alkylated adducts were obtained in quantitative yields. Tri-substituted β,γ-unsaturated esters, or in some case γ,δ-unsaturated esters, were obtained by the treatment of the alkylated adducts with EtMgCl. These procedures provide a good way for a new synthesis of di- and tri-substituted β,γ-unsaturated esters from aldehydes with two or three carbon–carbon bond-formations.

The silver salt of 12-tungstophosphoric acid: A mild and selective catalyst for the synthesis of β-ketoesters via C–H insertion

Abstract Aldehydes undergo smooth coupling with ethyl diazoacetate in the presence of 5 mol% silver substituted tungstophosphoric acid (AgTPA) under mild conditions to furnish β-ketoesters in high yields and with high selectivity via C–H insertion. This method is very useful for the preparation of β-ketoesters from both electron-rich as well as electron-deficient aromatic aldehydes. The catalyst can be recycled and reused for three to five subsequent runs with a gradual decrease of activity.

A new synthesis of β,γ-unsaturated esters from three components, aldehydes, chloromethyl p-tolyl sulfoxide, and tert-butyl acetate, via magnesium carbenoid 1,2-CH and 1,2-CC insertion as the key reaction

Addition reaction of 1-chlorovinyl p-tolyl sulfoxides, which were derived from various aldehydes, with lithium enolate of tert-butyl acetate at −78 °C in THF gave adducts in high yields. Magnesium carbenoids were generated by treatment of these adducts with Grignard reagents via the sulfoxide–magnesium exchange reaction. When the adducts were derived from alkyl aldehydes or electron-deficient aromatic aldehydes, carbenoid 1,2-CH insertion reaction took place from the magnesium carbenoids to afford β,γ-unsaturated butyric esters having a substituent at the β-position. On the contrary, when the adducts were derived from electron-rich aromatic aldehydes, carbenoid 1,2-CC insertion reaction took place from the magnesium carbenoids to give β,γ-unsaturated butyric esters having the aromatic group at the γ-position. Highly stereospecific 1,2-CC insertion reactions were observed in the latter reactions. This procedure provides a good way for a synthesis of β,γ-unsaturated esters from aldehydes with two carbon–carbon bond-formations.

Desymmetrizing 4-Substituted Cyclohexanones via Asymmetric Aldol Reaction

Herein, the authors report an asymmetric desymmetrization (ADS) of prochiral 4-substituted cyclohexanones via a proline amide catalyzed direct aldol reaction. In the reaction of 4-methyl cyclohexanone, the resulting aldol products with three stereogenic centers are obtained in moderate to good yields with excellent diastereo- (dr from 92:8 to >99:1) and high enantioselectivities (up to er >99.5:0.5). As aldehyde component, mainly electron-deficient aromatic aldehydes have been employed. The generality of the method could also be shown by varying the 4-substituent of the cyclohexanone. Synthetic application of the desymmetrization process has been illustrated by using the aldol products in subsequent transformations, e.g. Baeyer-Villiger reaction, with no loss of enantioselectivity.

Asymmetric Baylis-Hillman Reactions Catalyzed by Chiral Imidazolines

Chiral imidazolines are used to generate enantioenriched Baylis-Hillman products in the reaction of electron-deficient aromatic aldehydes with acrylates or alkyl vinyl ketones. The reaction generates the products in moderate to very good yield and in moderate enantioselectivities. Reactions without solvent were found to be optimal for acrylates, while the corresponding reaction with ketones is best run in toluene.

New N-terminal prolyl-dipeptide derivatives as organocatalysts for direct asymmetric aldol reaction

A series of new N-terminal prolyl-dipeptide derivatives have been synthesized and evaluated as organocatalysts for the direct asymmetric aldol reaction of acetone with electron-deficient aromatic aldehydes. At room temperature, the presence of 10 mol % of catalysts 2 and 5 efficiently catalyzes the direct asymmetric aldol reaction to give the aldol adducts with modest to excellent enantiomeric excesses (ee) values, which are up to 96%.

An efficient synthesis of β-amino esters via Zn(OTf) 2-catalyzed Mannich-type reaction

A Zn(OTf) 2-catalyzed Mannich-type reaction of the electron-deficient aromatic amines with the electron-deficient aromatic aldehydes and diethyl malonic ester was described. This three-component reaction afforded the corresponding β-amino esters in good yields.

(S)‐Histidine‐Based Dipeptides as Organic Catalysts for Direct Asymmetric Aldol Reactions.

The structure/activity relationships for some (S)-histidine-based dipeptide catalysts in direct aldol reactions have been examined. The reactivities and stereoselectivities are shown to be dependent upon the intramolecular cooperation of side-chain functional groups and the presence of a suitable combination and sequence of amino acids. Good yields (up to 96%) and enantioselectivities (up to 76% ee) were obtained with electron-deficient aromatic aldehydes in the presence of H-Leu-His-OH. The influence of different chiral and achiral co-catalysts on the reaction rates, yields and enantioselectivities has also been evaluated. Significant increases in the acceleration of the reaction, most remarkable for achiral trans-2,5-dimethylpiperazine as co-catalyst and the improved yields, were demonstrated.

( S)-Histidine-based dipeptides as organic catalysts for direct asymmetric aldol reactions

The structure/activity relationships for some ( S)-histidine-based dipeptide catalysts in direct aldol reactions have been examined. The reactivities and stereoselectivities are shown to be dependent upon the intramolecular cooperation of side-chain functional groups and the presence of a suitable combination and sequence of amino acids. Good yields (up to 96%) and enantioselectivities (up to 76% ee) were obtained with electron-deficient aromatic aldehydes in the presence of H-Leu-His-OH. The influence of different chiral and achiral co-catalysts on the reaction rates, yields and enantioselectivities has also been evaluated. Significant increases in the acceleration of the reaction, most remarkable for achiral trans-2,5-dimethylpiperazine as co-catalyst and the improved yields, were demonstrated.

Niobium(V) Chloride Catalyzed C—H Insertion Reactions of α‐Diazoesters: Synthesis of β‐Keto Esters.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Niobium(V) chloride-catalyzed C–H insertion reactions of α-diazoesters: synthesis of β-keto esters

Aldehydes react readily with ethyl diazoacetate in the presence of 5 mol% of NbCl 5 in dichloromethane to produce the corresponding β-keto esters in good yields with high selectivity. This method is very useful for the preparation of β-keto esters from both electron-rich as well as electron-deficient aromatic aldehydes under mild reaction conditions.

The First Series of Chiral 2,2′:6′,2′′‐Terpyridine Tri‐N‐Oxide Ligands for Lewis Base Catalyzed Asymmetric Allylation of Aldehydes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The first series of chiral 2,2':6',2''-terpyridine tri-N-oxide ligands for Lewis base-catalyzed asymmetric allylation of aldehydes.

The first series of chiral 2,2':6',2''-terpyridine tri-N-oxide ligands have been developed; They were showed to be active Lewis base-catalysts for asymmetric allylation of aldehydes using allyltrichlorosilane with optimal results at 0 degrees C for electron-deficient aromatic aldehydes (yields up to 97% and enantioselectivities up to 86% ee).