High Endo Selectivity Research Articles

Synthesis of highly functionalized 3,4-dihydro-2H-pyrans by high pressure lewis acid catalyzed cycloaddition of enol ethers and α,β-unsaturated aldehydes

New highly substituted 3,4-dibydro-2H-pyrans were synthesized with high ENDO selectivity by high pressure hetero Diels Alder reactions of α,β-unsaturated aldehydes and enol ethers in the presence of lanthanide-catalysts. Chiral induction was studied using chiral catalysts, a chiral enol ether and a combination of these chiralities.

Stereoselective synthesis of substituted tetrahydrofurans and butyrolactones by a new nickel catalyzed carbozincation

2-Iodo- and 2-bromoethyl allyl ethers undergo a highly diastereoselective ring closure producing trans-4,5-disubstituted lactols. After oxidation with m-chloroperbenzoic acid, trans-4,5-disubstituted butyrolactones (2-furanones) proceeds in satisfactory overall yield (45–56 %; >99% trans) for a range of substituted precursors 1 (R 2 = phenyl, n-hexyl or i-propyl). The use of cyclic 2-iodoacetals as precursors for the ring closure leads to new bicyclic heterocycles, such as 6a and 6b, with high endo-selectivity (>96% endo). An endo-selective preparation of a pyrrolidine is also reported ( endo >96%), although in this case, the intermediate zinc reagent could only be trapped effiently by deuterolysis, due to its low reactivity.

Polyimides by Diels‐Alder polyaddition of α‐pyrones

AbstractNew linear polyimides 11 were synthesized via Diels‐Alder addition polymerization of α‐pyrones 9 with bismaleimides 10. The number‐average molecular weights Mn range from 10 000 to 34 000 g. mol (gel‐permeation chromatography). The chemical structure of these polymers is supported by X‐ray crystallography, NMR spectra and model reactions. The Diels‐Alder addition occurred with high endo selectivity.

X‐Ray structures of endo and exo isomers of 6‐tert‐butyl‐2‐piperidone‐4,5‐(n‐phenyldicarboximide)

AbstractThe configuration of the two isomers obtained by the Diels‐Alder reaction of the 2‐azadiene I with N‐phenylmaleimide II (scheme) is established by X‐ray diffraction; The cycloaddition takes place with a high endo selectivity. The geometry of the two isomers is similar and the piperidone ring has a twist conformation in both molecules.

Lewis acid mediated Diels–Alder reactions of 2H-thiopyrans

Lewis acid mediated Diels–Alder reactions of 2H-thiopyrans with acrylate, crotonate, and methacrylate dienophiles have been investigated. Modest to good yields of predominantly exo adducts are obtained with 4-substituted 2H-thiopyrans. With 5-substituted 2H-thiopyrans, high endo selectivity is observed. No adducts were produced with methacrylate dienophiles. Relative to the thermal reactions, the exo selectivity is enhanced in the presence of Lewis acids. Unusually high exo selectivity is observed using "wet" Et2AlCl as the promoter.

High degree of exo selectivity in imino Diels-Alder reactions catalyzed by tert-butyldimethylsilyltriflate

Diels-Alder reactions of silyloxydiene 1 derived from 1-acetylcyclohexene with imines 2b and 2c occur with high exo selectivity depending upon experimental conditions: exo cycloadducts 3b–c are exclusively formed under kinetic control using tert-butyldimethylsilytriflate as catalyst. In the presence of AlCl 3, under thermodynamic control, high endo selectivity is only observed with 2b.

ChemInform Abstract: Facile Hetero‐Diels‐Alder Reaction of α,β‐Unsaturated Acyl Cyanides and Enol Ethers: Syntheses of 2‐Alkoxy‐3,4‐dihydro‐2H‐pyran‐6‐carbonitriles.

AbstractThe reaction of (I) or the nitrile generated in situ from (IV) with enol ethers (II) or (VII) proceeds with high endo selectivity to yield the title compounds (III), (VI) and (VIII)/(IX).

Synthesis and diels-alder reactions of 5,5-dicyanocyclopentadiene: regioselective synthesis of 1,5-disubstituted-1,3-cyclohexadienes

5,5-Dicyanocyclopentadiene, readily prepared in three steps from commercially available cis-1,4-dichloro-2-butene, undergoes Diels-Alder reactions with a number of dienophiles to give 5-substituted 7,7-dicyanobicyclo[2.2.1]hept-2-enes with high endo-selectivity. The adduct produced with methyl acrylate undergoes base-induced retro-Michael reactions to give 1-carbomethoxy-5-dicyanomethyl-1,3-cyclohexadiene.