Diels-Alder reactions 4+2 cycloaddition synthesis

This process, named the Diels-Alder cycloaddition reaction after its discoverers, is extremely useful in organic synthesis because it forms two carbon-carbon bonds in a single step and is one of the few genera) methods available for making cyclic molecules. (As the name implies, a cycloaddition reaction is one in which two reactants add together to give a cyclic product.) The... 

Synthesis of functionalized aryloxy 1,3-butadienes and their transformation to dienyl ethers via Diels-Alder cycloaddition reactions [136]... 

Details of various routes to allylphosphine oxides (43) have been reported, and the subsequent synthesis of 1,3-dienes has been illustrated by many examples.37 Also described are stereochemical aspects of these diene syntheses and of subsequent Diels-Alder cycloaddition reactions.37 High regioselectivity is observed in migrations of the diphenylphosphinoyl group from unsymmetrical sites, as in (44), in that both products have a double bond exocydic to the cyclohexane ring.38... 

Electron-deficient 1,3-dienes are potentially interesting Diels-Alder dienes. In our study with different kinds of olefins, we observed that 2-(phenylsulfonyl )-l,3-d1enes show a duality in their Diels-Alder cycloaddition reactions, giving [4+2] adducts with both electron-deficient and electron-rich olefins. This dual reactivity of the 2-(phenylsulfony1)-l,3-dienes in [4+2] cycloaddition increases the role they can play in organic synthesis. 

Flash vacuum pyrolysis has been used in the synthesis of 2ff-naphtho[l,2-f>]thiete 8 <98JHC1505> and benzobisthietes 9 and 10 <98TL9639>, and their Diels-Alder cycloaddition reactions have been studied. 

Finally, to highlight the advantages of both microwave-mediated protocols and solid-phase synthesis, a recently presented study48 is discussed in this chapter. This is the microwave-assisted solid-phase Diels-Alder cycloaddition reaction of 2(1 H)-pyrazinones with dienophiles (Scheme 7.43). 

Oxamborolidenes. There are noteworthy advances in the design, synthesis, and study of amino acid-derived oxazaborolidene complexes as catalysts for the Mukaiyama aldol addition. Corey has documented the use of complex 1 prepared from A-tosyl (S)-tryptophan in enantioselective Mukaiyama aldol addition reactions [5]. The addition of aryl or alkyl methyl ketones 2a-b proceeded with aromatic as well as aliphatic aldehydes, giving adducts in 56-100% yields and up to 93% ee (Scheme 8B2.1, Table 8B2.1). The use of 1-trimethylsilyloxycyclopentene 3 as well as dienolsilane 4 has been examined. Thus, for example, the cyclopentanone adduct with benzaldehyde 5 (R = Ph) was isolated as a 94 6 mixture of diastereomers favoring the syn diastereomer, which was formed with 92% ee, Dienolate adducts 6 were isolated with up to 82% ee it is important that these were shown to afford the corresponding dihydropyrones upon treatment with trifuoroacetic acid. Thus this process not only allows access to aldol addition adducts, but also the products of hetero Diels-Alder cycloaddition reactions. 

Kametani, T., Hibino, S., The Synthesis of Natural Heterocyclic Products by Hetero Diels-Alder Cycloaddition Reactions,... 

Heterocyclic iminium salts, oxidative transformation, 41, 275 Heterocyclic mesomeric betaines and analogs in natural product chemistry, 85, 67 Heterocyclic oligomers, 15, 1 Heterocyclic products, natural, synthesis of by hetero Diels-Alder cycloaddition reactions, 42, 245... 

Hetero Diels-Alder cycloaddition reactions, synthesis of natural heterocyclic products by, 42, 245... 

A facile synthesis of enantiopure tricyclic furyl derivatives employing 4-vinyl-2,3-dihydrofuran via Diels-Alder cycloaddition reaction was reported <02TL7983>. A new capture-ROMP-release procedure for chromatography-free purification of N-hydroxysuccinimide Mitsunobu reactions was reported by Hanson, who used a Mitsunobu reaction to capture a variety of alcohols onto a norbomenyl A-hydroxysuccinirmde monomer. Treatment of this monomer under ROM-polymerization then generated a water-soluble polymer that was readily separable from other by-products. Subsequent reaction with hydrazine was utilized to release the O-alkylhydroxylamines in good purity from the water-soluble polymer <020L1007>. 

Hetero Diels-Alder cycloaddition reactions, synthesis of natural heterocyclic products by, 42, 245 Heterodienophiles, new, heterocyclic synthesis using, 55, 1 Hilbert-Johnson reaction of 2,4-... 

Diels-Alder cycloaddition reactions in synthesis of natural heterocycles 87AHC(42)245. 

This article summarizes recent advances in the synthesis of natural products by hetero Diels-Alder cycloaddition reactions up to 1985. These recent disclosures have had a great impact on heterocyclic natural product syntheses. 

The first total synthesis of the marine furanosesquiterpenoid tubipofuran was accomplished in the laboratory of K. Kanematsu. The c/s-fused furanodecalin system was constructed by the regioselective Diels-Alder cycloaddition reaction of benzofuran quinone and Danishefsky s diene in refluxing toluene. The reaction gave an 11 1 mixture of the desired ortho-endo adduct versus the undesired para-endo product in 98% isolated yield. The major isomer then was subjected to sequential radical deoxygenation reactions before it was finally converted to the natural product. 

The critical step in the enantioselective and stereocontrolled total synthesis of eunicenone A by E.J. Corey et al. was the highly efficient chiral Lewis acid catalyzed intermolecular Diels-Alder cycloaddition reaction The diene component was mixed with 5 equivalents of 2-bromoacrolein and 0.5 equivalents of the chiral oxazaborolidine catalyst in CH2CI2 at -78 °C for 48h. The reaction gave 80% of the desired cycloadduct in 97% ee and the endolexo selectivity was 98 2. 

M. Shair and co-workers were the first to apply the enyne metathesis for macrocyclization during the biomimetic synthesis of (-)-longithorone A." The two 16-membered paracyclophane building blocks, one diene and one dienophile component, were prepared using 50 mol% Grubbs s first-generation catalyst under 1 atm ethylene gas pressure. These components, after several additional steps, underwent two facile Diels-Alder cycloaddition reactions to afford the natural product. 

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