Diels imino

Aza Diels-Alder Reactions of Azadienophiies 193 Tab, 5,3 Catalytic enantioselective aza Diels-Alder reactions using imino dienophiles (1)... 

Tab. 5.n Aza Diels-Alder reaction ofa-imino esters OSiMea... 

A chiral magnesium catalyst prepared from magnesium iodide and 1,2-diphenyl-ethylenediamine was also found to he effective in asymmetric aza Diels-Alder reaction of a-imino ester 21b with 7a (Scheme 5.12) [32]. The novel catalyst was discovered using parallel comhinatorial methods. 

Aza Diels-Alder Reactions of a-Imino Esters with Dienes 203... 

Imino Diels-Alder reactions catalyzed by indium trichloride (InCIs). Facile synthesis of quinoline and phenanthridinone derivatives [106]... 

The first enantioselective aza-Diels-Alder reactions of imino dienophiles on use of a chiral zirconium catalyst [116]... 

In contrast LP-DE gives disappointing results for intramolecular imino Diels-Alder reactions, even in the presence of CSA. This is due to the fact that weak acids become strong acids in highly polar media such as 5.0m LP-DE and the protonation of diene, with concomitant diene isomerization, competes with cycloaddition [42]. This observation was supported by using trifluoroacetic acid (TEA). The imine 33 (Scheme 6.21) in LP-DE at room temperature in the presence of TEA gave a 1 1 mixture of cycloadduct 34 and the isomerized diene 35 within the unreacted imine 33. No Diels-Alder cycloadduct 36 was detected. 

Catalysts such as Fe(BuEtCHC02)3 have been d eloped that are effective for the heteroatom Diels-Alder reaction. Indium trichloride (InCls) is a good catalyst for imino-Diels-Alder reactions. Hetero-Diels-Alder reactions involving carbonyls have been done in water. Ultrasound has been used to promote the Diels-Alder reactions of 1-azadienes. ... 

Oppolzer, W., Francotte, E., Battig, K. (1981) Total Synthesis of ( )-Lysergic Acid by an Intramolecular Imino-Diels-Alder Reaction. Helvetica ChimicaActa, 64, 478 81. 

On the other hand, novel diastereomeric p-amino thiol ligands possessing an isoquinuclidine skeleton have been readily prepared by Hongo et al. via imino-Diels-Alder reactions.As shown in Scheme 3.15, when applied to the enantioselective addition of ZnEt2 to various aldehydes, one of these ligands afforded the products with high enantioselectivities of up to 94% ee. 

As in the case of Diels-Alder reactions, aqueous aza-Diels-Alder reactions are also catalyzed by various Lewis acids such as lanthanide triflates.113 Lanthanide triflate-catalyzed imino Diels-Alder reactions of imines with dienes or alkenes were developed. Three-component aza-Diels-Alder reactions, starting from aldehyde, aniline, and Danishefsky s diene, took place smoothly under the influence of HBL4 in aqueous media to afford dihydro-4-pyridone derivatives in high yields (Eq. 12.46).114... 

Selective cyclization of an alkenyl imine is catalyzed by trimethylsilyl triflate (Scheme 76).329 /-Butyldimethylsilyl triflate ( BuN SiOTf) catalyzes imino Diels-Alder reactions of TV-phenyl-aromatic aldimines to afford exo adducts preferentially.330 When A1C13 is used instead of Bufv SiOTf, endo adducts are obtained predominantly. 

Jorgensen s group reported the aza Diels-Alder reactions in the presence of several chiral catalysts.52 They found that chiral bis(oxazoline) ligands 81, 83, 103, 104, and 105, which were effective in asymmetric oxo hetero Diels-Alder reactions, induced the aza Diels-Alder reaction of a-imino ester with Danishefsky s diene with only poor to moderate enantioselectivity. Selected results are listed in Scheme 5-40. 

On the other hand, the combination of Tol-BINAP with CUCIO4 has been shown to be very effective for aza Diels-Alder reactions. As shown in Scheme 5-41, moderate yield and good to excellent enantioselectivity can be obtained in the reaction of a-imino ester with diene 91 or 100. 

Another example, in which the piperidine cycle is generated de novo, exploits a hetero Diels-Alder cycloaddition of 1 -/r-tolylsulfinyl-1,3-penta-diene 91 with benzylnitrosoformate, that generates an oxazine 92 with complete regioselectivity and 7i-facial diastereoselectivity.69 Osmilation of the double bond inserts stereoselectively two hydroxyl groups on the oxazine skeleton, protection and catalytic hydrogenation finally afforded the enantiomerically pure imino sugars 94 (Fig. 38). 

Fig. 38 Synthesis of imino sugars via Diels-Alder cycloaddition on sulfinyl pentadiene. Reagents and conditions (a) CH2Cl2, -78 °C to 0 °C (b) 0s04, NMO (c) DMP, PTSA (d) Pd/C, H2 (e) ClC02Bn.

In addition, iodine snccessfnlly catalyzed the electrophilic snbstitntion reaction of indoles with aldehydes and ketones to bis(indonyl)methanes [225], the deprotection of aromatic acetates [226], esterifications [227], transesterifications [227], the chemoselective thioacetalization of carbon functions [228], the addition of mercaptans to a,P-nnsatnrated carboxylic acids [229], the imino-Diels-Alder reaction [230], the synthesis of iV-Boc protected amines [231], the preparation of alkynyl sngars from D-glycals [232], the preparation of methyl bisnlfate [233], and the synthesis of P-acetamido ketones from aromatic aldehydes, enolizable ketones or ketoesters and acetonitrile [234],... 

Diels-Alder, imino dienophiles, 65, 2 Diels-Alder, intramolecular, 32, 1 Diels-Alder, maleic anhydride, 4, 1 [4 -h 3], 51, 3 of enones, 44, 2 of ketenes, 45, 2 of nitrones and alkenes, 36, 1 Pauson-Khand, 40, 1 photochemical, 44, 2 retro-Diels-Alder reaction, 52, 1 53, 2 [6-h4], 49, 2 [3-h2], 61, 1 Cyclobutanes, synthesis ... 

Imidates, rearrangement of, 14, 1 Imines, additions of allyl, allenyl, propargyl stannanes, 64, 1 additions of cyanide, 70, 1 as dienophiles, 65, 2 synthesis, 70, 1 Iminium ions, 39, 2 65, 2 Imino Diels-Alder reactions, 65, 2 Indoles, by Nenitzescu reaction, 20, 3 by reaction with TosMIC, 57, 3 Ionic hydrogenation, 71, 1 Isocyanides, in the Passerini reaction, 65, 1... 

Babu G, Perumal PT (1998) Indium trichloride (InCl3) catalyzed imino Diels-Alder reactions an efficient synthesis of cyclopentaquinolines, azabicyclooctanones and azabicyclo-nonanones. Tetrahedron 54 1627-1638... 

Although several Lewis acids are known to catalyze the hetero-Diels-Alder reaction involving imino-dienes or imino-dienophiles (aza-Diels-Alder reaction), a large amount of the catalyst is often necessary. Bi(0Tf)3-xH20 showed higher activity than lanthanide triflates in catalyzing the reactions of imines with Danishefsky s diene (Scheme 15) [72]. 

The precursor to (5) was made diastereoselectively by Fessner and coworkers [44]. When the intermediate ketose 1-phosphate was immediately submitted to hydrogenation conditions, l,5,6-trideoxy-l,5-imino-D-galactitol (1,6-dideoxygalactonojirimycin, 10) was obtained in fair yield [42]. The latter derivative was also obtained by a hetero Diels-Alder cycloaddition of a benzyloxycarbonyl nitroso dienophile to ( , )-sorbaldehyde dimethylacetal [45]. 

The preparation of piperidines by cycloaddition can use either an imino (Scheme 13) or azadiene (Scheme 14) substrate. Highly functionalized tetrahydropiperidines were prepared by a high-pressure aza-Diels-Alder reaction <99TL1877>. The hetero [4+2] cycloaddition of vinyl... 

An unprecedented nitrogen elimination reaction of 4-amino-7-benzylpyrrolo [23- f][133]triazine-5-caibonitrile (72) to give the pyrrole derivative 74 has been described. The following mechanism, presumably via a a retro Diels-Alder reaction of the imino tautomer 73, has been proposed <990L537>. 

A synthesis of ( )-tylophorine (213) has been based on the discovery that vanadyl trifluoride (VOF3) can be used to convert 1,2-diarylethylene into phenanthrenes in high yield. In the top sequence shown in Scheme 34, ring closure is accompanied by dehydrogenation (77CC826). In a second synthesis, ( )-tylophorine (213) is the result of an intramolecular version of a Diels-Alder cycloaddition of a conjugated diene with an imino dienophile (Scheme 34, lower sequence) (79JA5073). 

Other classical synthetic approaches to 2-furanamine have failed, including the Curtius method and Beckmann rearrangement of 2-benzoylfuran oxime. However, hydrazinolysis of AT-(2-furyl)phthalimide, obtained from phthalimide and 2,5-dimethoxy-2,5-dihy-drofuran, gives 2-furanamine which was not isolated but detected by GLC-MS and H NMR spectroscopy. The latter reveals the absence of imino tautomers (75AP713). The chemistry of 2-dialkylamino-5-phenylfurans is typical of enamines protonation occurs on carbon to produce iminium salts. They are stable to base but afford 5-phenylfuran-2(3//)-one on hydrolysis with dilute acid. 2-Morpholino-5-phenylfuran couples with diazonium salts and affords Diels-Alder adducts with maleic anhydride and IV-phenylmaleimide (73JCS(P1)2523). 

Imino Diels-Alder reactions.1 The cycloaddition of dihydro-p-carbolines with... 

Imino Diels-Alder reactions. The neurotoxic fungal toxin slaframine (2) has been synthesized by an intramolecular imino Diels-Alder reaction. The substrate is obtained from the amide 1 via a methylol derivative. These derivatives are best prepared by reaction of the amide with Cs2C03 and paraformaldehyde in dry THF (equation I). When heated they lose acetic acid and undergo cyclization. 

IMINO DIELS-ALDER REACTIONS Cesium carbonate. 

The seco-phenanthroindolizidine alkaloid septicine has been synthesized by a nitrone route. A cycloaddition of 1-pyrroline 1-oxide with 2,3-bis-(3,4-dimethoxyphenyl)butadiene gives two stereoisomeric isoxazolidines, one of which is converted into ( ) septicine.10 ( )-Tylophorine and 5-coniceine have been prepared by a new route that makes use of an intramolecular imino-Diels-Alder reaction.11 A stereoselective synthesis of 3,5-dialkyl-indolizidines has been applied to the synthesis of a stereoisomer of the trail pheromone of the Pharaoh ant and to a stereoisomer of gephyrotoxin 223.12 A stereoselective total synthesis of ( )-perhydrogephyrotoxin (21)13 and a simple synthesis of ( )-gephyran14 have been reported. 

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