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A series of unsymmetrically substituted diastereoisomeric (Ra,R) and (Sa,R) bipyridine N,N′‐dioxides was synthesized by using oxidative coupling of the corresponding metallated tetrahydroisoquinoline N‐oxides in the presence of iodine. The N,N′‐dioxides contained substituted aryl groups with electron‐donating or electron‐accepting groups in the near vicinity of the N,N′‐dioxide moiety. Their catalytic activity was tested in a series of reactions of allyltrichlorosilane with various substituted benzaldehydes, thiophenecarbaldehyde, and cinnamaldehyde. The reactions proceeded with high enantioselectivities (up to 98 % ee) with catalyst loadings as low as 0.5 mol‐%. Furthermore, allylation reactions of (E)‐3‐iodomethacrylaldehyde were also carried out to give chiral (E)‐1‐iodo‐2‐methylpenta‐1,4‐dien‐3‐ol, a convenient building block for the synthesis of natural products. The allylations proceeded with high enantioselectivities (up to ca. 99 % ee) with a catalyst loading of 2.5 mol‐%. A series of unsymmetrically substituted diastereoisomeric (Ra,R) and (Sa,R) bipyridine N,N′‐dioxides were tested as catalysts for the enantioselective allylation of various aldehydes. Homoallylic alcohols were obtained with enantiopurities of up to 99 % ee. [ABSTRACT FROM AUTHOR]

The first asymmetric total synthesis of coibacin D, a metabolite isolated from the marine cyanobacterium cf. Oscillatoria sp., was achieved in six steps starting from simple hept-6-en-1-ol. The synthetic strategy was based on a chiral Brønsted acid catalyzed enantioselective allylboration and a Ru-carbene complex catalyzed sequential ring-closing and cross-metathesis strategy. The recorded spectroscopic data and the sign of the optical rotation of the synthesized coibacin D were in agreement with the published data for the isolated compound, which confirmed the proposed structure and absolute configuration. [ABSTRACT FROM AUTHOR]

A comparative study of the catalytic allylations and crotylations of ( E)- and ( Z)-haloacrylaldehydes by Lewis bases (chiral N, N′-dioxides) and Brønsted acids (chiral phosphoric acids) was undertaken. The reactions proceeded with high enantio- and diastereoselectivities with slightly better asymmetric induction observed in the case of N, N′-dioxide catalysis. The formed enantioenriched chiral unsaturated haloalcohols could be considered general building blocks, as they could be used in the syntheses of more complex natural products possessing substituted 1,3-diene fragments. This was exemplified by the formal total syntheses of pteronenone and antillatoxin. [ABSTRACT FROM AUTHOR]

The cyclization of various enynes with the Negishi reagent provides the corresponding bicyclic zirconacyclopentenes, which after exposure to allyl chloride in the presence of a catalytic amount of cop-per(I) chloride, undergo bisallylation to furnish 1,9-decadienes in good yields (42-89%). The dienes are subjected to ring-closing metathesis to afford bicyclic compounds with [6.3.0]bicycloundecane (8,5-fused ring system) or [6.4.0]bicyclododecane (8,6-fused ring system) frameworks in good to excellent yields (52-92%). Selective monoallylation of a selected zirconacyclopentene followed by carboxyethylation with ethyl chloroformate gives rise to the corresponding ester, which after meta-lation and reaction with allyl bromide, furnishes a 1,9-decadiene. Ring-closing metathesis then yields the expected eight-membered cyclic product in 92% yield. This procedure constitutes a new pathway to bicyclic carbocyclic systems starting from 1,ω-enynes. [ABSTRACT FROM AUTHOR]

The key aetheramide A intermediate with the natural (R,R,R) configuration along with the one having the unnatural (R,S,R) configuration was synthesized. The synthesis of both stereoisomers was accomplished by Suzuki coupling of two advanced chiral building blocks: (R,R)- and (R,S)-vinylboronates and an (R)-iodoalkene. The former was prepared from (R)- mandelic acid, and the latter was prepared by enantioselective allylation of 3-iodoacrylaldehyde. [ABSTRACT FROM AUTHOR]

Allylation, trans- and cis-crotylation of (2 E,4 E)-2,4-dimethylhexadienal, a representative α,β,γ,δ-unsaturated aldehyde, was carried out under different catalytic and stoichiometric conditions. The reactions catalyzed by organocatalysts TRIP-PA and N, N′-dioxides gave the best results with respect to yields, asymmetric induction, and catalyst load in comparison to other procedures. The developed methodology was applied in the enantioselective synthesis of (5 R,6 S)-(+)-pteroenone, a defensive metabolite (ichthyodeterrent) of the Antarctic pteropod Clione antarctica. [ABSTRACT FROM AUTHOR]

Various enantioselective allylations and crotylations of tert-butyldimethylsilyl-protected vanillin were undertaken to assess the best methodology to provide the corresponding homoallylic alcohols in high yields with high enantiopurity. In general, most of the tested allylations proceeded with high enantioselectivities (>92 % ee) and in the case of crotylation also with excellent diastereoselectivity (96 % ee, >98 % de). The product obtained from the crotylation reaction was used in the enantioselective synthesis of the unnatural diastereoisomer of a recently isolated lignan derivative. [ABSTRACT FROM AUTHOR]

We report a systematic study of the allylation of ortho-substituted benzaldehydes under catalysis of a Lewis base ( N, N-dioxide), a Lewis acid (Keck allylation), and a Brønsted acid. ortho-Halobenzaldehydes were used as the aldehydic substrates, and special attention was paid to ortho-vinyl and alkynyl benzaldehydes, which might serve as interesting synthons for the preparation of more complex chiral compounds. Similar enantioselectivities were achieved under catalytic conditions. In the case of ortho-halobenzaldehydes, Lewis base catalysis proved to be more efficient, and the highest asymmetric induction for allylation of ortho-fluorobenzaldehyde reached 82 % ee, which is comparable to other used catalytic conditions. In cases of ortho-vinylbenzaldehyde, the Keck allylation provided the product in 88 % ee. An enantioenriched homoallylic alcohol was used as the starting material for the synthesis of a sertraline intermediate. [ABSTRACT FROM AUTHOR]

The enantioselective allylation of an aromatic aldehyde to give a chiral homoallylic alcohol was employed as the key step in the syntheses of a flobufen metabolite and dapoxetine. In the former case, the homoallylic alcohol moiety (99 % ee) was converted into a five-membered lactone ring with good preservation of the optical purity, and the target compound, a flobufen metabolite, was obtained in 95 % ee. In the latter case, the homoallylic alcohol moiety (97 % ee) was transformed over several steps into a 3-aminopropanol moiety. During the course of the synthesis, the gradual loss of optical purity was observed, and the target compound, dapoxetine, was obtained in 85 % ee. [ABSTRACT FROM AUTHOR]

The enantioselective allylation of thiophene-2-carbaldehyde with allyltrichlorosilane under Lewis base catalysis has been studied. The use of catalytic amount (1 mol%) of chiral bipyridine N,N′-dioxides provided the corresponding 1-(thiophen-2-yl)-but-3-en-1-ol with asymmetric induction reaching 97% ee. The prepared chiral ( S)-1-(thiophen-2-yl)-but-3-en-1-ol was used as the crucial chiral building block in a formal total synthesis of duloxetine. [ABSTRACT FROM AUTHOR]

N-oxides possessing the pyridine framework are strong Lewis bases that can activate the C-Si bond of allylhalosilanes to such an extent that they catalyze reactions with aldehydes. N-oxides embedded in chiral scaffolds are usually capable of highly selective chirality transfer to the derived products. Our goal was to develop a general synthetic method allowing the preparation of structurally varied N,N'-dioxides suitable for enantioselective organocatalysis. The underlying synthetic strategy was based on [2 + 2 + 2]-cyclotrimerization of suitably substituted diynes with nitriles catalyzed by Co-complexes to generate the desired bipyridines, their further oxidation and resolution of which furnished the corresponding chiral N,N'-dioxides. The prepared compounds were used in catalytic allylation of aromatic aldehydes to homoallyl alcohols with high enantioselectivity (up to 96 % ee). Enantioselectivity, enantiodiscrimination, and the reaction mechanism are controlled by the choice of solvent. [ABSTRACT FROM AUTHOR]

A new class of axially chiral bipyridine N,N′-oxides with bis(tetrahydroisoquinoline) framework were tested as catalysts in the reaction of aliphatic aldehydes with allyl(trichloro)silane to afford homoallylic alcohols. The course of the reaction, that is, the catalytic activity as well as enantioselectivity, is strongly dependent on the solvent used. The products were obtained in good yields and up to 68% ee in chloroform. [ABSTRACT FROM AUTHOR]

One pathway for the preparation of enantiomerically pure compounds from prochiral substrates is the use of metal complex catalysis with chiral ligands. Compared to the other frequently used chiral ligands, chiral 2,2′-bipyridines have been underexploited, despite the data indicating that such ligands have considerable potential in synthetic chemistry. One of those is the so-called Bolm's ligand, a compound possessing chiral alcohol moieties in the side chains attached to the 2,2′-bipyridine scaffold. Various metal salts have been used in combination with Bolm's ligand as potent catalysts able to bring about enantioselective alkylations, allylations, conjugate additions, desymmetrization of meso-epoxides, aldol reactions, etc. This review aims to summarize Bolm's ligand applications in the area of enantioselective synthesis over the last three decades since its preparation. [ABSTRACT FROM AUTHOR]

An abstract of the article "Bisallylation of Zirconacyclopentenes and Ring-Closing Metathesis: A Route to Eight-Membered-Ring Compounds" by Nikola Topolovcan and colleagues is presented.

Enantioselective allylation and crotylation of tert-butyldimethylsilyl protected vanillin proceeds with high asymmetric induction by using different catalytic systems. [ABSTRACT FROM AUTHOR]

Optimized reaction conditions are developed for the enantioselective allylation of thiophen-2-carbaldehyde. [ABSTRACT FROM AUTHOR]

The TIBP-catalyzed allylation of β-iodoacrylaldehyde (I) with crotylboronic acid ester (II) gives rise to chiral iodoalcohol (III), which is converted by Suzuki-Miyaura cross-coupling reaction into intermediates (V) of the natural compounds pteroenone (VI) and antillatoxin (VII). [ABSTRACT FROM AUTHOR]

The enantioselective allylation of aldehydes (I) and (VIII) with pinacolborane (II) in the presence of a chiral BINOL-phosphoric-acid-derived catalyst is the key step in the synthesis of the flubofen metabolite (VII) and dapoxetine (X). [ABSTRACT FROM AUTHOR]