Unsymmetrical Dienes Research Articles

Theoretical Investigation on Regioselectivities of Diels‐Alder Reactions by Conjugated Effect

Summary of main observation and conclusionThe regioselectivities of 76 Diels‐Alder reactions between unsymmetrical dienes and dienophiles were investigated by local softness and generalized local softness at atomic and chemical bond view, respectively, where the reactivity descriptors were calculated by finite difference approximation and ABEEMσπ model. Based on local HSAB principle and matching criterion of local softness, reasonable explanation and prediction on regioselectivities of all reactions through ABEEMσπ model have been obtained, which are in agreement with the experimental results. Especially, at π‐bond level, while the 1‐substituents of dienes were NH2, NMe2, and NEt2, because of the p‐π conjugated effect between the lone pairs of N atom and the conjugated π‐bond of the four double‐bonded carbon atoms in diene, it made the dienophile not easy to approach diene by Manner A, hence, Manner B can forecast the ortho regioisomer as main product well, and Manner A cannot. As to the other reactions, both Manner A and Manner B can predict their regioselectivities. It can be seen that the ABEEMσπ model can take the effect of the chemical environment on the reaction reactivity into account richly, especially the system includes π‐bond and lone pairs. However, the results through the finite difference approximation are not reasonable.

MESO-PROPYLENE-CO-ETHYLENE POLYOLEFIN RUBBER: VULCANIZATION AND COMPARISON TO AMORPHOUS STEREOISOMER RUBBER

ABSTRACT A new class of polyolefin rubbers containing a majority of propylene copolymerized with ethylene and a vulcanizable, unsymmetrical diene is described. The key structural feature of these rubbers is the presence of meso-propylene sequences, which leads to a small level of crystallinity, which is amplified on uniaxial tensile deformation. This strain induced crystallization leads to very remarkable tensile and tear properties in sulfur and resin vulcanized formulations, even for very low viscosity compounds. Isomeric rubbers of a similar composition but with irregular propylene sequences, which are and stay amorphous on extension, are unremarkable in their vulcanized properties.

Synthesis of substituted allyl acetates from heterocyclic dienes by Pd-promoted arylation-acetoxylation cascade

Pd-catalysed arylation?acetoxylation cascade, a previously reported methodology, was applied in the functionalisation of unsymmetrical dienes. Both explored classes of compounds, isoquinoline and ?-carboline-derived dienes, afforded single regioisomers. Although further improvements of the process are necessary, primarily due to lower yields, the described functionalisation of the studied compounds might be useful in the synthesis of emetine and related naturally occurring compounds.

Ni‐Catalyzed Asymmetric Cycloisomerization of Dienes by Using TADDOL Phosphoramidites

A library of α,α,α,α-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL)-based phosphoramidites has been synthesized and applied in the Ni-catalyzed cycloisomerization of different dienes. Through the systematic variation of the three structural motifs of the lead structure, that is, the amine moiety, the protecting group, and the aryl substituents, the ligand features could be optimized for the asymmetric cycloisomerization of the model substrate diethyl diallylmalonate. The substrate scope of the new catalytic system was extended to other diallylic substrates, including unsymmetrical dienes. Overall remarkably high activities of up to approximately 13 500 h(-1) , very high selectivities toward five-membered exo-methylenecyclopentanes, and enantioselectivities of up to 92 % ee have been achieved.

Palladium-Promoted [2 + 2 + 2] Cocyclization of Arynes and Unsymmetrical Conjugated Dienes: Synthesis of Justicidin B and Retrojusticidin B

A facile synthesis of natural and unnatural arylnaphthalenes has been demonstrated via the unprecedented palladium-promoted [2 + 2 + 2] cocyclization of arynes and unsymmetrical conjugated dienes using the N-heterocyclic carbene as a ligand. The unsymmetrical dienes used herein are actually α-coupled acrylate-cinnamate combinations bearing two β-positive carbons and follow the key [2 + 2 + 2] cocyclization pathway.

ChemInform Abstract: Substrate‐Controlled Regioselective Cobalt(I)‐Catalyzed 1,4‐Hydrovinylation Reactions.

AbstractThe regioselectivity of unsymmetrical dienes is controlled by the steric hindrance of the substituents in 2‐ and 3‐position.

Syntheses of structurally diverse amino acids, including δ-hydroxylysine, using the acyl nitroso Diels–Alder reaction

Abstract By virtue of its ability to introduce amino and hydroxy functionalities in a 1,4-relationship with fully controlled relative stereochemistry, the acyl nitroso Diels–Alder (ANDA) reaction is ideally suited to the synthesis of structurally diverse, including hydroxylated, amino acids. The major issue to be tackled is that of regiochemistry in the ANDA addition to unsymmetrical dienes. The transformation of three diverse types of ANDA adducts into amino acids is described, in particular, the synthesis of δ-hydroxylysine, an important constituent of collagen, as a single (2SR, 5SR) diastereoisomer in protected form.

Activation of N-Sulfonyl Oxaziridines Using Copper(II) Catalysts: Aminohydroxylations of Styrenes and 1,3-Dienes

N-Sulfonyl oxaziridines are susceptible to electrophilic activation using copper(II) catalysts and react with styrenes under these conditions to provide 1,3-oxazolidines in a formal aminohydroxylation of the alkene. We propose a two-step mechanism involving a cationic intermediate to account for the rate differences and regioselectivities observed using a variety of styrenes. In accord with our hypothesis, aminohydroxylations of a range of substrates bearing electron-stabilizing groups are successful, and 1,3-dienes are particularly good substrates for copper(II)-catalyzed aminohydroxylation. Reactions of unsymmetrical dienes provide good to excellent olefin selectivity, the sense and magnitude of which can be rationalized upon consideration of the stability of the cationic intermediates suggested by our mechanism. Diastereoselective synthesis of a diverse range of densely functionalized structures can be achieved by polyfunctionalization of dienes using aminohydroxylation as a key complexity-increasing step.

Synthesis of Silylallene Glycosides and Diene Diglycosides by C‐Glycosidation of D‐Glucal with 1,4‐Bis(trimethylsilyl)‐2‐butyne.

Silylmethylallenyl glycosides, symmetrical and unsymmetrical diene glycosides, were synthesized by C-glycosidation with 1,4-bis(trimethylsilyl)-2-butyne in good yield. The nature of the product is controlled by the choice of Lewis acid, BF3·OEt2, or SnCl4. The efficient construction of unsymmetrical diene glycosides was achieved in one pot on the basis of the order of addition of sugar starting materials.

An efficient construction of a C3-symmetric macrocycle by head to tail cyclotrimerization of an unsymmetrical diene via a sequence of highly regio- and stereoselective metathesis reactions

A sequence of highly regio- and stereoselective intermolecular metatheses followed by ring-closing metathesis of an 1-allyl-3-(3-butenyl)cyclohexanol led to a C 3-symmetric head to tail cyclic trimer; a 24-membered macrocycle containing three inward directed hydroxyl groups creating a hydrophilic cavity.

Synthesis of Silylallene Glycosides and Diene Diglycosides by C-Glycosidation of d-Glucal with 1,4-Bis(trimethylsilyl)-2-butyne

[reaction: see text] Silylmethylallenyl glycosides, symmetrical and unsymmetrical diene glycosides, were synthesized by C-glycosidation with 1,4-bis(trimethylsilyl)-2-butyne in good yield. The nature of the product is controlled by the choice of Lewis acid, BF(3).OEt(2), or SnCl(4). The efficient construction of unsymmetrical diene glycosides was achieved in one pot on the basis of the order of addition of sugar starting materials.

Enantioselective and Structure‐Selective Diels—Alder Reactions of Unsymmetrical Quinones Catalyzed by a Chiral Oxazaborolidinium Cation. Predictive Selection Rules.

The chiral oxazaborolidinium cation 1 promotes Diels−Alder reactions between 2-triisopropylsilyloxy-1,3-butadiene and a number of unsymmetrical 1,4-benzoquinones in a highly enantioselective and structurally selective manner. The basis for the enantioselectivity is explained rationally in terms of a preferred type of transition-state assembly. Selection rules have been developed that allow the prediction of the principal reaction product of Diels−Alder reaction between unsymmetrical diene and quinone components.

Enantioselective and Structure-Selective Diels−Alder Reactions of Unsymmetrical Quinones Catalyzed by a Chiral Oxazaborolidinium Cation. Predictive Selection Rules

The chiral oxazaborolidinium cation 1 promotes Diels-Alder reactions between 2-triisopropylsilyloxy-1,3-butadiene and a number of unsymmetrical 1,4-benzoquinones in a highly enantioselective and structurally selective manner. The basis for the enantioselectivity is explained rationally in terms of a preferred type of transition-state assembly. Selection rules have been developed that allow the prediction of the principal reaction product of Diels-Alder reaction between unsymmetrical diene and quinone components.

Electrostatic control of the regioselectivity in the photoisomerization of trans,trans-1-fluoro-2,4-hexadiene: evidence for competing conical intersections.

trans,trans-1-Fluoro-2,4-hexadiene (EE-FHD) was used to explore the excited potential energy surfaces of acyclic 1,3-dienes. Our investigations show that the regioselectivity of double-bond photoisomerization is primarily controlled by the charge-stabilizing characteristic of substituents on the double bonds of the diene. Furthermore, changes in the photoregioselectivity with solvent polarity suggest that the excited unsymmetrical diene returns to the ground state by competing pathways which traverse polarized 1Bu states and drop into two different conical intersections

Synthesis of a 1,3‐Spiro‐amino‐alcohol‐derived Chiral Auxiliary and Its Application to Diels—Alder Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of a 1,3-spiro-amino-alcohol-derived chiral auxiliary and its application to Diels–Alder reactions

A short synthesis and resolution of (1 R,5 R,6 R)-6-aminospiro[4.4]nonan-1-ol, 11, is reported. The pivalamide derivative (+)- 5 gives excellent diastereo- and regiocontrol as well as endo selectivity as a chiral auxiliary in the BCl 3-catalyzed Diels–Alder reaction with a variety of symmetrical and unsymmetrical dienes. The adducts are readily cleaved by saponification, allowing recovery and reuse of (+)- 5.

The Diels—Alder Reactivity of (E)‐3‐Phenylsulfonylprop‐2‐enenitrile, a Cyanoacetylene Equivalent.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Diels–alder reactions of anthracenes with C‐sulfonyldithioformates

AbstractC‐Sulfonyldithioformates (2) (R1 = ArSO2, R2 = ArS) readily add to anthracene and 9‐methylanthracene (1) in a Diels–Alder fashion with formation of 9,10‐dihydro‐10,9‐(epithiomethano)anthracenes (3) which in turn may suffer thermally induced elimination of arenesulfinic acid to yield the 9‐anthracenedithiocarboxylic esters (4). The reactions with the unsymmetrical diene 9‐methylanthracene take place in a highly stereoselective fashion. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:170–174, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10119

The Diels–Alder reactivity of (E)-3-phenylsulfonylprop-2-enenitrile, a cyanoacetylene equivalent

(E)-3-Phenylsulfonylprop-2-enenitrile undergoes facile Diels–Alder reactions, moderate regioselectivity being observed with several unsymmetrical dienes. Danishefsky's diene and furfuryl alcohol react regioselectively. The cycloadducts formed with cyclopentadiene and with anthracene undergo base-catalysed elimination of benzenesulfinic acid to yield α,β-unsaturated nitriles.

Synthesis of New Captodative Alkenes: Alkyl 2-Aroyloxy Acrylates − Structure, and Reactivity in Diels−Alder Cycloadditions

Novel captodative alkenes, namely the methyl and ethyl esters of 2-aroyloxyacrylic acids, 2 and 3, have been prepared. Their reactivity and selectivity have been evaluated in Diels−Alder cycloadditions with unsymmetrical dienes, which generate the corresponding adducts with high regioselectivity. No significant stereoselectivity was observed in the reaction with cyclopentadiene (9), although Lewis acid catalysis improved the exo/endo isomeric ratio. Structural and electron spectroscopic studies of these alkenes are supported by MO calculations. FMO theory accounts for the regioselectivity observed with isoprene (7), and the reactivity seen in Diels−Alder additions correlates with the stabilization of the relevant vacant π* MO in these alkenes, which is mainly due to the electron-withdrawing group.