Cyanoethylations and Michael additions. II. The synthesis of allylic cyclohexenols by γ-cyanoethylation of α,β-unsaturated aldehydes and ketones. Part II

1970 ◽  
Vol 48 (18) ◽  
pp. 2819-2838 ◽  
Author(s):  
Ch. R. Engel ◽  
J. Lessard
Keyword(s):  
Membered Ring ◽  
Detailed Report ◽  
Michael Additions ◽  
Unsaturated Aldehydes ◽  
Single Operation ◽  
Aldehydes And Ketones ◽  
High Yields

The detailed report of the first cyclo-γ-cyanoethylation of an α,β-unsaturated carbonyl system, 3β-acetoxy-5α-pregn-17-en-21-al, is given. This reaction, which proceeds in high yields, gives rise, in a single operation, to products with an additional functionalized six-membered ring, primarily to allylic α′-cyanohexenols.

Cyanoethylations and Michael additions. IV. The synthesis of allylic cyclohexenols by γ-cyanoethylation of α, β-unsaturated aldehydes and ketones. Part IV

1970 ◽  
Vol 48 (20) ◽  
pp. 3136-3143 ◽  
Author(s):  
Ch. R. Engel ◽  
L. Ruest
Keyword(s):  
Cotton Effect ◽  
Membered Ring ◽  
Main Reaction ◽  
Ring Size ◽  
Reaction Products ◽  
Double Bonds ◽  
Michael Additions ◽  
Unsaturated Aldehydes ◽  
Aldehydes And Ketones

The cyclo-γ-cyanoethylation of 3β-acetoxy-D-homo-5α-pregn-17a-en-21-al is reported. It is shown that the orientation of the cyanoethylation of 2-cycloalkyl-substituted ethenals does not significantly depend on the ring size of the cycloalkyl substituent. It is further shown that the stereochemistry of the cyclohexadienonitrile obtained by dehydration of the main reaction products seems to be, in the case of a fusion to a six-membered ring, in agreement with Moscowitz' rule relating the helicity of the chromophore to the sign of its Cotton effect, in contradistinction to the situation in the case of a system in which one of the double bonds of the chromophore is exocyclic to a five-membered ring.

Cyanoethylations and Michael additions. V. The synthesis of allylic cyclohexenols by γ-cyanoethylation of α,β-unsaturated aldehydes and ketones. Part V

1970 ◽  
Vol 48 (21) ◽  
pp. 3425-3439 ◽  
Author(s):  
Ch. R. Engel ◽  
V. S. Salvi ◽  
L. Ruest
Keyword(s):  
Reaction Time ◽  
Steric Hindrance ◽  
Carbonyl Compounds ◽  
Transfer Reaction ◽  
Main Reaction ◽  
Reaction Products ◽  
Enol Ethers ◽  
Michael Additions ◽  
Unsaturated Aldehydes ◽  
Aldehydes And Ketones

It is shown that the cyanoethylation of 3β-acetoxy-21-methyl-5α-pregn-17-en-21-one results in part in the addition of acrylonitrile to the γ-position, with concomitant cyclization, and that therefore the cyclo-γ-cyanoethylations of α,β-unsaturated carbonyl compounds reported previously were not confined to aldehydes. However, the main reaction products of the conjugated ketone were α-cyanoethylated derivatives. A variation of the reaction time did not affect the proportion of α- and γ-cyanoethylated products; the implications of this finding on mechanistic considerations are discussed; in particular, an explanation based on the assumption of an equilibrium between reactants and α- and γ-cyanoethylated products is ruled out. It is shown that the γ-additions observed, particularly in the case of α,β-unsaturated aldehydes, are not due to steric hindrance, neither to an abnormal charge distribution in the anion. It is further shown that in the presence of base the propionitrile moiety of oxygen-cyanoethylated α,β-unsaturated aldehydes with a suitable geometry is transferred to the γ-position of the original aldehyde and that cyclization occurs so that the same products are obtained from such cyano-enol ethers as in the direct cyanoethylation of the free aldehydes. On the basis of this finding, a mechanism for the cyclo-γ-cyanoethylations of α,β-unsaturated carbonyl compounds, involving such a transfer reaction, can be tentatively proposed.

Hafnium(IV) Chloride Catalyzes Highly Efficient Acetalization of Carbonyl Compounds

2019 ◽  
Vol 16 (6) ◽  
pp. 913-920 ◽  
Author(s):  
Israel Bonilla-Landa ◽  
Emizael López-Hernández ◽  
Felipe Barrera-Méndez ◽  
Nadia C. Salas ◽  
José L. Olivares-Romero
Keyword(s):  
Microwave Heating ◽  
Reaction Times ◽  
Protecting Groups ◽  
Catalyst Loading ◽  
Selective Protection ◽  
Highly Efficient ◽  
Aldehydes And Ketones ◽  
High Yields ◽  
Novel Catalyst ◽  
Acid Labile

Background: Hafnium(IV) tetrachloride efficiently catalyzes the protection of a variety of aldehydes and ketones, including benzophenone, acetophenone, and cyclohexanone, to the corresponding dimethyl acetals and 1,3-dioxolanes, under microwave heating. Substrates possessing acid-labile protecting groups (TBDPS and Boc) chemoselectively generated the corresponding acetal/ketal in excellent yields. Aim and Objective: In this study. the selective protection of aldehydes and ketones using a Hafnium(IV) chloride, which is a novel catalyst, under microwave heating was observed. Hence, it is imperative to find suitable conditions to promote the protection reaction in high yields and short reaction times. This study was undertaken not only to find a novel catalyst but also to perform the reaction with substrates bearing acid-labile protecting groups, and study the more challenging ketones as benzophenone. Materials and Methods: Using a microwave synthesis reactor Monowave 400 of Anton Paar, the protection reaction was performed on a raging temperature of 100°C ±1, a pressure of 2.9 bar, and an electric power of 50 W. More than 40 substrates have been screened and protected, not only the aldehydes were protected in high yields but also the more challenging ketones such as benzophenone were protected. All the products were purified by simple flash column chromatography, using silica gel and hexanes/ethyl acetate (90:10) as eluents. Finally, the protected substrates were characterized by NMR 1H, 13C and APCI-HRMS-QTOF. Results: Preliminary screening allowed us to find that 5 mol % of the catalyst is enough to furnish the protected aldehyde or ketone in up to 99% yield. Also it was found that substrates with a variety of substitutions on the aromatic ring (aldehyde or ketone), that include electron-withdrawing and electrondonating group, can be protected using this methodology in high yields. The more challenging cyclic ketones were also protected in up to 86% yield. It was found that trimethyl orthoformate is a very good additive to obtain the protected acetophenone. Finally, the protection of aldehydes with sensitive functional groups was performed. Indeed, it was found that substrates bearing acid labile groups such as Boc and TBDPS, chemoselectively generated the corresponding acetal/ketal compound while keeping the protective groups intact in up to 73% yield. Conclusion: Hafnium(IV) chloride as a catalyst provides a simple, highly efficient, and general chemoselective methodology for the protection of a variety of structurally diverse aldehydes and ketones. The major advantages offered by this method are: high yields, low catalyst loading, air-stability, and non-toxicity.

scholarly journals Theoretical Insight into the Reversal of Chemoselectivity in Diels-Alder Reactions of α,β-Unsaturated Aldehydes and Ketones Catalyzed by Brønsted and Lewis Acids

Organics ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 38-49
Author(s):  
Lakhdar Benhamed ◽  
Sidi Mohamed Mekelleche ◽  
Wafaa Benchouk
Keyword(s):  
Lewis Acids ◽  
Major Product ◽  
Diels Alder ◽  
Unsaturated Ketone ◽  
Unsaturated Aldehydes ◽  
Aldehydes And Ketones ◽  
Theoretical Insight ◽  
Insight Into ◽  
Good Agreement

Experimentally, a reversal of chemoselectivity has been observed in catalyzed Diels–Alder reactions of α,β-unsaturated aldehydes (e.g., (2E)-but-2-enal) and ketones (e.g., 2-hexen-4-one) with cyclopentadiene. Indeed, using the triflimidic Brønsted acid Tf2NH as catalyst, the reaction gave a Diels–Alder adduct derived from α,β-unsaturated ketone as a major product. On the other hand, the use of tris(pentafluorophenyl)borane B(C6F5)3 bulky Lewis acid as catalyst gave mainly the cycloadduct of α,β-unsaturated aldehyde as a major product. Our aim in the present work is to put in evidence the role of the catalyst in the reversal of the chemoselectivity of the catalyzed Diels–Alder reactions of (2E)-but-2-enal and 2-Hexen-4-one with cyclopentadiene. The calculations were performed at the ωB97XD/6-311G(d,p) level of theory and the solvent effects of dichloromethane were taken into account using the PCM solvation model. The obtained results are in good agreement with experimental outcomes.

scholarly journals Copper(I) Chloride/Kieselguhr: A Versatile Catalyst for Oxidation of Alkyl Halides and Alkyl Tosylates to the Carbonyl Compounds

1999 ◽  
Vol 23 (7) ◽  
pp. 434-435
Author(s):  
Mohammed M. Hashemi ◽  
Yousef Ahmadi Beni
Keyword(s):  
Carbonyl Compounds ◽  
Alkyl Halides ◽  
Aldehydes And Ketones ◽  
High Yields

Copper(I) Chloride adsorbed on Kieselguhr in the presence of oxygen catalyses oxidation of alkyl halides and alkyl tosylates to the aldehydes and ketones in high yields.

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