Alder Cycloadducts Research Articles

An Efficient Route to Pentasubstituted Phenols

AbstractA simple and convenient three‐step protocol for the synthesis of pentasubstituted tribromophenols based on the acid‐catalyzed Grob‐type fragmentation of the bicyclic ketone precursors 8a–e in high overall yield is described. The bicyclic ketones 8a–e were obtained in two steps starting from the Diels–Alder cycloadducts 5a–e of β‐substituted vinyl acetates and tetrabromo‐5,5‐dimethoxycyclopentadiene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

PtCl 2-Promoted cyclopropane opening in [4+2+2] homo Diels–Alder cycloadducts

A new and readily available catalytic system has been developed to open the cyclopropane ring in [4+2+2] homo Diels–Alder cycloadducts formed by reaction of norbornadienes and 1,3-butadiene. The cobalt-mediated homo Diels–Alder reaction followed by this PtCl 2-promoted isomerization is a key step in the efficient route to bicyclo[5.3.0]decanes, core of numerous natural products.

Cis–trans Enantiomerism in the Diels–Alder cycloadducts of 6-arylfulvenes with maleic anhydride: resolution of the exo adducts via the N-((1S)-1-(naphth-1-yl)ethyl)imide derivatives: assignment of the absolute configurations based on the crystal structure of an imide diastereomer

A new case of the uncommon cis–trans enantiomerism is presented. The titled anhydride adducts were prepared in good yields by the known reaction of three 6-arylfulvenes with maleic anhydride (aryl=phenyl, p-tolyl and p-anisyl). The exo adducts were converted to the corresponding imides by reaction with (1S)-1-(naphth-1-yl)ethylamine in ∼80% yields, and the resulting diastereomeric imides separated by silica gel column chromatography. They were hydrolysed and recyclised to the chiral anhydrides, in ‘one-pot’ with 10% NaOH–EtOH, followed by treatment with 2M HCl, in ∼40% yields. The titled anhydrides were thus obtained in homochiral form, in enantiomeric purities (generally) of ∼90% as indicated by chiral HPLC. The chiral anhydrides were also converted to the corresponding imides (presumably stereospecifically), by treatment with ammonia solution in excellent yields. The crystal structure of one of the above diastereomeric imides (derived from 6-phenylfulvene) was determined, and based on the known (S)-configuration of the naphthylethylamine moiety, the ‘configurations’ of the original anhydride adducts were assigned.

5-Nitro[2.2]paracyclophanepyran-6-one—building block for the synthesis of [2.2]paracyclophanes containing condensed benzofuran subunits

The 5-nitro[2.2]paracyclophanepyran-6-one 2 has been synthesized. DBN treatment of the Diels–Alder cycloadducts of 2 followed by DDQ oxidation unexpectedly led to [2.2]paracyclophanes containing a condensed benzofuran subunit.

Chromone-3-carboxaldehydes in Diels–Alder reactions with indole- o-quinodimethane. Synthesis of tetrahydrochromeno[2,3- b]carbazoles

An efficient route to a new class of indole derivatives, tetrahydrochromeno[2,3- b]carbazoles, has been developed. The cycloaddition reactions of chromone-3-carboxaldehydes with indole- o-quinodimethane gave a diastereomeric mixture of Diels–Alder cycloadducts in good yields after in situ deformylation.

An Efficient One‐Pot Synthesis of Phenol Derivatives by Ring Opening and Rearrangement of Diels—Alder Cycloadducts of Substituted Furans Using Heterogeneous Catalysis and Microwave Irradiation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enantiomerically pure Diels–Alder cycloadducts from aldohexose-derived dihydropyranones

The thermal and Et 2O·BF 3-catalyzed Diels–Alder additions of 2,3-dimethylbutadiene and cyclopentadiene to (2 S,6 S)-6-acetoxymethyl-2-(2-propyloxy)-2 H-pyran-3(6 H)-one 1, derived from d-galactose, afforded the corresponding enantiomerically pure tetrahydrobenzopyrones resulting from the addition of the diene to the α or β face of 1. The facial and endo– exo selectivities in the formation of the adducts, and their yields, are influenced by the diene and the reaction conditions employed. In particular, low overall yields were obtained in the Lewis acid-promoted reactions. This was attributed to the presence of a Lewis base (an acetoxymethyl group) in the pyranone 1. Therefore, (2 R,6 S)-6-methyl-2-(2-propyloxy)-2 H-pyran-3(6 H)-one 7, which possesses a C-6 methyl substituent instead of an acetoxymethyl, was prepared from l-fucose and subjected to the Et 2O·BF 3-catalyzed addition of cyclopentadiene. As expected, a good yield (74%) of the corresponding Diels–Alder product was obtained, with excellent β- and endo-diastereoselectivities.

Tandem or Sequential Coupling‐IMDA Cycloaddition Approach to Highly Fused Polycarbocycles.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel sulfoxide-introducing reaction and photochromic reactions of ethenylsulfinyl derivatives of dithienylethenes

New diarylethenes possessing one or two arenesulfinylethenyl moieties were casually synthesised. The photochromic and chiroptical properties of 1,2-bis-2-{2-methyl-5-[2-(4-toluenesulfinyl)ethenyl]-3-thienyl}-3,3,4,4,5,5-hexafluorocyclopentene were examined. While its colouring quantum yield by 313-nm irradiation ( Φ O→ C ) was as large as 0.46, its bleaching quantum yield by 621-nm irradiation ( Φ O→ C ) was negligibly small. Diels–Alder reaction of 2-(4-toluenesulfinyl)-1,4-benzoquinone with diarylethenes with the structure of 1-aryl-2-(5-ethenyl-2-methyl-3-thienyl)-3,3,4,4,5,5-hexafluorocyclopentene gave, instead of the expected Diels–Alder cycloadduct or its derivatives, 1-aryl-2-{2-methyl-5-[2-(4-toluenesulfinyl)ethenyl]-3-thienyl}-3,3,4,4,5,5-hexafluorocyclopentene.

Tandem Diels—Alder Cyclization/Aromatization Reactions of 5‐Vinyl‐1‐acyl‐2‐aryl‐2,3‐dihydro‐4‐pyridones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Simple preparation of cobaloxime dienyl complexes and their exo selective Diels–Alder cycloadducts : Progress toward transition metal-mediated Diels–Alder reactions which are catalytic in metal dienyl complex

A new method for the synthesis of cobaloxime dienyl complexes (cobaloxime=pyridine(dimethylglyoxime) 2Co) which involves a zinc-mediated hydrocobaltation of enynes is reported. Use of this dienyl complex synthesis method allows subsequent Diels–Alder reactions of these complexes to be accomplished without isolation of the dienyl complexes. A new silane-based cobaloxime-substituted cycloadduct demetallation protocol is then reported which provides Diels–Alder cycloadducts and cobalt complexes which have been recycled into the zinc-mediated dienyl complex synthesis.

Cycloaddition of methyl 2-(2,6-dichorophenyl)-2 H-azirine-3-carboxylate to electron-rich 2-azadienes

tert-Butyldimethylsililoxy-2-aza-1,3-butadienes react with 2 H-azirine 3 leading to Diels–Alder cycloadducts in moderate yields. The reactions are endo- and regioselective with the azirine being added by its less hindered face. There is only one product in the case of 1b , 4b . There are two isomers ( 4 and 5 ) from 1a , 1c and 1d . A different result was obtained with the diene 1e . Diene 1e formed products 4e and 8 . Some of compounds 4 and 5 have been hydrolysed leading to functionalised aziridines 7 . Compound 8 gave aziridine 9 .

First General Approach to Cyclohex‐3‐ene‐1,1‐bis(phosphonates) by Diels—Alder Cycloaddition of Tetraethyl Vinylidenebis(phosphonate) to 1,3‐Dienes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Stereo‐ and Regioselectivity of Pd0/InI‐Mediated Allylic Additions to Aldehydes and Ketones. In situ Generation of Allylindium(III) Intermediates from N‐Acylnitroso Diels—Alder Cycloadducts and 1‐Amino‐4‐acetoxycyclopentenes.

Acylnitroso Diels-Alder cycloadduct (11, 37, and 45)- and cyclopentenyl acetate (8 and 9)-derived allylindium(III) species were generated in situ from palladium(0) catalysts and indium(I) iodide, and the stereo- and regiochemistry of their additions to aldehydes and ketones were investigated. Solvent, catalyst, and ionic effects were examined for the reaction of N-acetyl cycloadduct (11) and benzyloxyacetaldehyde (10). The solvent mixture of THF/H(2)O with Pd(OAc)(2).PPh(3) catalysis was found to be optimal. The addition of N-acetyl cycloadduct to aliphatic aldehydes afforded products in good yields and high regio- and stereoselectivity, with the cis-1,4-isomers constituting 90-95% of the products. The reactions with N-Boc (37a) and N-methylcarbamate (37b) cycloadducts also gave the cis-1,4-products predominantly. The same regio- and stereoselectivity applied to the reactions of 4-acetoxy-1-(N-hydroxyphenyacetamido)cyclopentene (8). 4-Acetoxy-1-phenylacetamidocyclopentene (9), however, afforded trans-1,4-products exclusively. Mechanistic speculations involving chelated transition states are described.

Tandem Diels–Alder cyclization/aromatization reactions of 5-vinyl-1-acyl-2-aryl-2,3-dihydro-4-pyridones

A tandem Diels–Alder cyclization/aromatization of 5-vinyl-2,3-dihydro-4-pyridones and various dienophiles is reported. The intermediate Diels–Alder cycloadduct undergoes an elimination/aromatization to provide β-amino-ketones, β-amino-alcohols, and unnatural amino acids containing useful functionality.

Cycloaddition of o‐Quinodimethanes Generated from 1,2‐Bis(bromomethyl)benzenes by Constant‐Current Electroreduction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Unexpected condensation reaction of two units of 1,2‐dihydrophosphinine 1‐oxides in the presence of tetracyanoethylene

AbstractIn the presence of tetracyanoethylene, the reaction of two molecules of dihydrophosphinine oxide 2B followed an unexpected route to afford diphosphatricyclododecatrienes 4 instead of the corresponding Diels–Alder cycloadducts (3). Structures of the products (4) have been elucidated by a joint application of spectroscopy and quantum chemical calculations. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:29–35, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10062

Cycloaddition of o-Quinodimethanes Generated from 1,2-Bis(bromomethyl)benzenes by Constant-Current Electroreduction

Abstract The constant-current electroreduction of 1,2-bis(bromomethyl)benzenes with dienophiles in NH4NO3–MeOH gave Diels–Alder cycloadducts in moderate-to-good yields.

4,5-Dehydrooctafluoro[2.2]paracyclophane: facile generation and extraordinary Diels–Alder reactivity

Dehydroiodination of 4-iodo-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane by treatment with KO t Bu in the presence of benzene, naphthalene, anthracene, or t- butylbenzene affords each of the corresponding Diels–Alder cycloadducts of the presumed aryne intermediate in high yield. The products were characterized by their NMR spectra, with one of them also being confirmed by X-ray crystallography. The extraordinary selectivity/reactivity of the aryne intermediate is discussed. Graphic

ChemInform Abstract: Novel 1,4‐Benzodiazepines from Acylnitroso‐Derived Hetero‐Diels—Alder Cycloadducts.

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