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.

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.

Ring Opening Metathesis Polymerization of Norbornene by WCl6: Formation of WCl5 and WCl4 and Their Catalytic Activity

1996 ◽  
Vol 61 (9) ◽  
pp. 1353-1359 ◽  
Author(s):  
Hynek Balcar ◽  
Zdeněk Bastl
Keyword(s):  
Catalytic Activity ◽  
Ring Opening ◽  
Main Reaction ◽  
Reaction Products ◽  
Double Bonds ◽  
Ring Opening Metathesis Polymerization ◽  
Chlorine Atoms ◽  
Metathesis Polymerization ◽  
Xps Spectroscopy ◽  
Tungsten Species

Reaction between WCl6 and norbornene in benzene and cyclohexane, respectively, was investigated using UV/VIS, ESR and XPS spectroscopy in order to establish the main reaction products on the tungsten side and their relation to the initiation of ring opening metathesis polymerization (ROMP) of norbornene. The tungsten compounds: WCl5, insoluble WCl4 and soluble tungsten species having four chlorine atoms bound to tungsten, [WCl4Ln] were found to be the main products. The catalytic activity of the respective compounds in ROMP of norbornene was found to decrease in the order: WCl5 > WCl6 >> WCl4 ~ [WCl4Ln]. The polynorbornenes prepared with both WCl4 and [WCl4Ln] possess higher content of cis double bonds in comparison with polymers prepared with WCl6 and WCl5 catalysts.

On the Reaction of 2,5-Dihydroxy-[1,4]-benzoquinone with Diamines – Strain-induced Reactivity Effects

2020 ◽  
Vol 24 ◽  
Author(s):  
Hubert Hettegger ◽  
Andreas Hofinger ◽  
Thomas Rosenau
Keyword(s):  
Nucleophilic Substitution ◽  
Product Structure ◽  
Carbonyl Groups ◽  
Reaction Products ◽  
Double Bonds ◽  
Oh Groups ◽  
Natural Geometry ◽  
Quinoid Structure ◽  
Bond Localization

: The regioselectivity of the reaction of 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) with diamines could not be explained satisfactorily so far. In general, the reaction products can be derived from the tautomeric ortho-quinoid structure of a hypothetical 4,5-dihydroxy-[1,2]-benzoquinone. However, both aromatic and aliphatic 1,2-diamines form in some cases phenazines, formally by diimine formation on the quinoid carbonyl groups, and in other cases the corresponding 1,2- diamino-[1,2]-benzoquinones, by nucleophilic substitution of the OH groups, the regioselectivity apparently not following any discernible pattern. The reactivity was now explained by an adapted theory of strain-induced bond localization (SIBL). Here, the preservation of the "natural" geometry of the two quinoid C–C double bonds (C3=C4 and C5=C6) as well as the N–N distance of the co-reacting diamine are crucial. A decrease of the annulation angle sum (N–C4–C5 + C4–C5–N) is tolerated well and the 4,5-diamino-ortho-quinones, having relatively short N–N spacings are formed. An increase in the angular sum is energetically unfavorable, so that diamines with a larger N–N distance afford the corresponding ortho-quinone imines. Thus, for the reaction of DHBQ with diamines, exact predictions of the regioselectivity, and the resulting product structure, can be made on the basis of simple computations of bond spacings and product geometries.

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.

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