Buta-1.3-diene Diels-Alder reactions with

An extensive review of the hetero-Diels-Alder reactions of 1-oxabuta-1,3-dienes has been published. Ab initio calculations of the Diels-Alder reactions of prop-2-enethial with a number of dienophiles show that the transition states of all the reactions are similar and synchronous.Thio- and seleno-carbonyl compounds behave as superdienophiles in Diels-Alder reactions with cyclic and aryl-, methyl-, or methoxy-substituted open-chain buta-1,3-dienes.The intramolecular hetero-Diels-Alder reactions of 4-benzylidine-3-oxo[l,3]oxathiolan-5-ones (100) produce cycloadducts (101) and (102) in high yield and excellent endo/exo-selectivity (Scheme 39). A density functional theoretical study of the hetero-Diels-Alder reaction between butadiene and acrolein indicates that the endo s-cis is the most stable transition structure in both catalysed and uncatalysed reactions.The formation and use of amino acid-derived chiral acylnitroso hetero-Diels-Alder reactions in organic synthesis has been reviewed. The 4 + 2-cycloadditions of A-acylthioformamides as dienophiles have been reviewed. ... 

An AMI semiempirical method was used to investigate the Diels-Alder cycloaddition reactions of vinyl sulfenes with buta-1,3-dienes.156 The reactivity and stereoselectivity of vinyl boranes have been reviewed.157 Aromatic methyleneamines undergo reverse-electron-demand Diels-Alder reactions with cyclopentadiene, norbom-ene, and vinyl sulfides.158... 

A DFT study of the polar Diels-Alder reaction of 4-aza-6-nitrobenzofuroxan with cyclopentadiene found only one highly asynchronous transition state structure associated with the formation of the 4 + 2-adduct.178 4-Nitrobenzodifuroxan has been shown to be a highly reactive nitroalkene in Diels-Alder reactions with common dienes (cyclopentadiene) to produce stable NED adducts and with ethyl vinyl ether to produce IED adducts.179 Unlike a-acylfuran, 2-nitrofurans have been shown to be active dienophiles in thermal NED Diels-Alder reactions with a variety of buta-1,3-dienes, including Danishefsky s diene.180... 

The regiochemistry of Diels-Alder reactions with 3.3.3-trifluoropropene (1) shows that the inductive effect of a trifluoromethyl group increases the magnitude of the molecular orbital coefficient of the unsubstituted terminus, but the effect is not great enough to achieve high regioselectivity with dienes other than l-methoxy-3-(trimethylsiloxy)buta-l,3-diene (Danishefsky s diene, 4) compare the reaction of 1 with 2, 3, and 4. ... 

Diels-Alder reaction with support-bound 4-[3-(tert-butyldimethylsilyloocy)buta-l,3-die-nyl] groups (Scheme 65) [310] N-[(Fluoren-9-ylmethoxycarbonyl)ethyl]maleimide (304) (135 mg, 0.375 mmol) was weighed into a screw-cap vial (Reacti-Vial) and toluene (800 pL) was added. The vial was sealed and heated until the dienophile dissolved, and resin bearing a diene (302 or 306) was added and allowed to swell in reagent and solution. The vial was sealed and kept at 110 °C overnight The reaction solution was drained and the resin washed as follows ... 

Oxidation of pyridazino[4,5-d]pyridazine-l,4-diol (3) with lead(IV) acetate yields the unstable l,4-dihydropyridazino[4,5-<7]pyridazine-l,4-dione. The formation of this compound could be demonstrated by its Diels-Alder reaction with anthracene or buta-1,3-diene.12... 

Sol 2. (i) Butadiene sulfone or 3-sulfolene, a solid, is a convenient substitute for gaseous buta-1,3-diene. Diels—Alder reaction between buta-1,3-diene and dienophiles with low reactivity usually requires prolonged heating above 100 °C. This makes a procedure rather dangerous, if neat buta-1,3-diene is used, and requires special equipment for work under elevated pressure. Alternatively, buta-1,3-diene can be generated in situ by thermal sulfur dioxide extrusion from sulfolene, in which case no buildup of buta-1,3-diene pressure could be expected as the liberated diene is consumed in the cycloaddition, and, therefore, the equilibrium of the reversible extrusion reaction acts as an internal safety valve. ... 

Cyclo-octa-l,5-diyne, prepared in 2% yield by dimerization of buta-l,2,3-triene, has been examined by X-ray diffraction and shown to be almost planar with C—C C bond angles of 159.3°. Irradiation of cyclo-octa-l,5-diyne gave buta-l,2,3-triene, and treatment with ba gave cyclo-octa-tetraene. Cyclo-octa-l,5-diyne underwent Diels-Alder reactions with two molecules of buta-1,3-diene and 2,3-dimethylbuta-1,3-diene, but gave complex mixtures of products when treated with bromine, iodine, dimethyl acetylenedicarboxylate, or tcne. ... 

Diene Adduct. 3-Trimethylsilyl-3-buten-2-one undergoes a Shapiro reaction to give the 2,3-bis(trimethylsilyl)buta-1,3-diene in 32% yield (eq 7). This compound undergoes Diels-Alder reactions with a number of dienophiles (e.g. maleic anhydride, ben-zoquinone) in benzene at 60 °C to give sUylated cycloaddition adducts. ... 

Compounds containing a double or triple bond, usually activated by additional unsaturation (carbonyl, cyano, nitro, phenyl, etc.) In the ap position, add to the I 4-positions of a conjugated (buta-1 3-diene) system with the formation of a ax-membered ring. The ethylenic or acetylenic compound is known as the dieTwphile and the second reactant as the diene the product is the adduct. The addition is generally termed the Diels-Alder reaction or the diene synthesis. The product in the case of an ethylenic dienophile is a cyctohexene and in that of an acetylenic dienophile is a cyctohexa-1 4-diene. The active unsaturated portion of the dienophile, or that of the diene, or those in both, may be involved in rings the adduct is then polycyclic. 

The Diels-Alder reaction catalyzed by this chiral titanium catalyst 31 has wide generality (Scheme 1.53, 1.54, Table 1.22, 1.23). Acryloyl- and fumaroyl-oxazolidinones react with isoprene giving cycloadducts in high optical purity. 2-Ethylthio-l,3-buta-diene can also be successfully employed as the diene [42]. 

Pseudo-/ -DL-gi Zopyranose triacetate (36) was prepared by hydroxyla-tion of the enetriol triacetate (32) and converted to the corresponding pentol and pentaacetate. The intermediate 32 was obtained by Diels-Alder reaction (200°C., two days) of rans/ rans-l,4-diacetoxy-l,3-buta-diene with allyl acetate. The double bond was surprisingly inert to the usual additive reagents and not detectable by infrared spectroscopy because of near-symmetry, but it did react with tert-butyl hydroxperoxide to give 36 in about 30% yield (27). 

The scope and efficiency of [4+2] cycloaddition reactions used for the synthesis of pyridines continue to improve. Recently, the collection of dienes participating in aza-Diels Alder reactions has expanded to include 3-phosphinyl-l-aza-l,3-butadienes, 3-azatrienes, and l,3-bis(trimethylsiloxy)buta-l, 3-dienes (1,3-bis silyl enol ethers), which form phosphorylated, vinyl-substituted, and 2-(arylsulfonyl)-4-hydroxypyridines, respectively <06T1095 06T7661 06S2551>. In addition, efforts to improve the synthetic efficiency have been notable, as illustrated with the use of microwave technology. As shown below, a synthesis of highly functionalized pyridine 14 from 3-siloxy-l-aza-1,3-butadiene 15 (conveniently prepared from p-keto oxime 16) and electron-deficient acetylenes utilizes microwave irradiation to reduce reaction times and improve yields <06T5454>. 

The reactions of 4-nitrobenzodifuroxan 242 with a series of common dienes, such as cyclopentadiene, cyclohexa-diene, isoprene, 2,3-dimethylbutadiene, and 1-acetoxybutadiene, with ethoxymethyleneacetylacetone were found to proceed very readily to afford stable cycloadducts, which are the result of highly stereoselective normal electron-demand (NED) Diels-Alder reactions. Due to the additional activation provided by the two adjacent furoxan rings, the nitroalkene double bond of compound 242 is also prone to undergo NED reactions with less reactive dienic structures, such as the enol form of ethoxymethyleneacetylacetone and the in situ generated 2-ethoxy-4-(2-furfur-yl)buta-l,3-diene <2004TL1037, 2005T8167>. 

Ab initio calculations on aza-Diels-Alder reactions of electron-deficient imines with buta-l,3-diene show that these reactions are HOMO (diene)-LUMO(dienophile)-controlled and that electron-deficient imines should be more reactive than alkyl-or aryl-imines. The Diels-Alder reaction of r-butyl 2//-azirine-3-carboxylate (80) proceeds with high diastereoselectivity with electron-rich dienes (81) (Scheme 28). The hetero-Diels-Alder additions of imines with sterically demanding dienes yield perhydroquinolines bearing an angular methyl group. The asymmetric hetero-Diels-Alder reaction between alkenyloxazolines and isocyanates produces diastereometri-cally pure oxazolo[3,2-c]pyrimidines. °... 

Steric factors have been shown to be important in controlling the face sensitivities in 4 + 2-cycloadditions of diastereotopically non-equivalent n -facial 1,6-annulated-cyclohexa-1,3-dienes.102 The diastereoselectivity of the Diels-Alder reactions of l-(f-butyldimethylsiloxy)buta-1,3-diene with C(2) symmetric tartrate-derived dienophiles... 

A DFT study on the oxa-Diels-Alder reaction of buta-1,3-diene with formaldehyde, catalysed by Co(II) and Co(III) complexes, has shown that axial coordination of an... 

Like other Diels-Alder reactions, reactions involving 2-trimethylsilyloxy-buta-1,3-dienes proceed under good stereochemical control. In the examples depicted in Equation Si3.12 and Si3.13, the dienophiles react with the dienes through conventional endo transition states to give exclusively endo adducts. 

Stable disilenes generally do not undergo Diels-Alder cycloaddition with conjugated dienes16, but the reaction is well known in the cases of more reactive disilene derivatives8. The stereochemistry of the reaction has not been widely studied, but isolated examples such as those shown in equations 86-88 show that the reaction proceeds with retention of the original stereochemistry of both the diene (equation 88)161 and the disilene (equations 86 and 87)162. Reaction of tetrakis(trimethylsilyl)disilene (35) with 1,3-buta-diene in solution yields the expected Diels-Alder adduct 116 (equation 89)68. 

Lewis acid catalysis for aza Diels-Alder reactions of 2-aza-l,3-butadienes [254], In analogy to the hitherto discussed aza Diels-Alder reactions, evidence for a non-concerted mechanism of these transformations has emerged. Thus, Mellor et al. have found that under suitable conditions azaanthraquinone 3-34 does not only form the expected cycloadduct 3-37 upon treatment with a-methylstyrene and formaldehyde, but the tertiary alcohol 3-36 is also generated presumably via cation 3-35. Alcohol 3-36 is easily converted into the cycloadduct 3-37 and 3-35 is therefore supposed to act as intermediate in a non-concerted multistep sequence (Fig. 3-12) [255,256]. More recent studies on N-arylimines performed by Laschat et al. have corrobated the assumption that non-concerted processes represent a noteworthy mechanistic pathway in reactions of 2-aza-l,3-buta-dienes with suitable dienophiles [257]. 

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