Diels-Alder dienes 2- Acetoxy-1,3-butadiene

Diels-Alder dienes 1-Acetoxybutadiene. Butadiene. Cyclopentadiene. (rans,mins-l,4-Diacetoxybutadiene. 2,5-Di-o-anisyl-3,4-diphenylcyclopentadienone. 5,5-Dimethoxy-l, 2,3,4-tetrachlorocyclopentadienone. 2,3-Dimethylbutadiene. 6,6-Dimethylfulvene (see o-Acetoxy acrylonitrile). 2,4-Dimethyl-l,3-pentadiene (see Diethyl azodicarboxylate). 2,3-Diphenyl-butadiene. 1,3-Diphenylisobenzofurane (see Potassium I-butoxide). rrans,/nus-l,4-Diphenyl-butadiene. 1,3-Diphenylisobenzofurane. Hexachlorocyclopentadiene. Isobenzofurane. l-o-Nitrophenylbutadiene-1,3. Oxepin (see Diazabicyclo[3.4.0]nonene-S). Phenylcyclone. Piperylene. n-Pyrone (see also Methyl vinyl ketone). Tetrachlorocyclopentadienone. Tetra-chlorofurane. Tetraphenylcyclopentadienone. 

The presence of the catalyst can also favor multiple Diels-Alder reactions of cycloalkenones. Two typical examples are reported in Schemes 3.6 and 3.7. When (E)-l-methoxy-1,3-butadiene (14) interacted with 2-cyclohexenone in the presence of Yb(fod)3 catalyst, a multiple Diels-Alder reaction occurred [21] and afforded a 1 1.5 mixture of the two tricyclic ketones 15 and 16 (Scheme 3.6). The sequence of events leading to the products includes the elimination of methanol from the primary cycloadduct to afford a bicyclic dienone that underwent a second cycloaddition. Similarly, 4-acetoxy-2-cyclopenten-l-one (17) (Scheme 3.7) has been shown to behave as a conjunctive reagent for a one-pot multiple Diels-Alder reaction with a variety of dienes under AICI3 catalysis, providing a mild and convenient methodology to synthesize hydrofluorenones [22]. The role of the Lewis acid is crucial to facilitate the elimination of acetic acid from the cycloadducts. The results of the reaction of 17 with diene... 

Chiral boron catalysts had already been widely used in a variety of reactions before they were applied in Diels-Alder reactions220. Boron catalysts were first employed in the Diels-Alder reactions of quinones with electron-rich dienes. Kelly and coworkers221 found that stoichiometric amounts of a catalyst prepared from BH3, acetic acid and 3,3 -diphenyl-l,l/-bi-2-naphthol (344) catalyzed the reaction of 1-acetoxy-l,3-butadiene (341) with juglone (342) to afford cycloadduct 343 with 98% ee (equation 96). The reaction was supposed to proceed via a spirocyclic borate complex in which one face of the double bond of juglone was effectively shielded from attack by the diene. 

A number of other specific reactions have been studied. For example, Diels-Alder reactions of the unsaturated 5(4//)-oxazolone derived from piperonal with 2-ferf-butyldimethylsilyloxy-1,3-butadiene, piperylene, 1-acetoxy-1,3-butadiene, and Danishefsky s diene have been described. In these cases, the results are variable and are dependent on the diene with poor yields often obtained even at high temperatures. Moreover, the stereochemical outcome of these reactions has not been determined. " ... 

New possibilities in hetero-Diels-Alder condensation have been opened by the introduction of highly active l-methoxy-3-trimethylsilyloxy-, 4-benzoyIoxy-l-methoxy-3-trimethylsilyloxy-, and 2-acetoxy-l-alkoxy-3-trimethylsilyloxy-l,3-butadienes ( Danishefsky dienes, 5). These compounds readily react under atmospheric pressure, in the presence of Lewis acids, with normal aldehydes (e.g., acetaldehyde, benzaldehyde, furfural) to furnish 2,3-disubstituted or 2,3,5-trisubstituted derivatives of 2,3-dihydro-4H-pyran-4-one 7 capable of readily functionalizing to sugars (Scheme 5) [26]. This approach... 

Dichlorobis(diisopropoxy)titanium(IV). Titanium(IV) chloride. Zinc iodide. DIELS-ALDER REACTIONS 2-Acetoxy-I-methoxy-3-trimethylsilyloxy-1,3-butadiene. 4-Acetoxy-1 -trimethylsilyl-1,3-butadiene. Benzyl irans-l,3-butadiene-l-carbamate. 1,3-Bis(/-butyldimethylsilyloxy)-2-aza-1,3-diene. 2,3-Bis(trimethylsilyl)methyl-1.3-buladiene (10-1,3-Dimethoxybutadiene 4-I)iniethyhnnino 1,1,2... 

Excellent selectivities were observed in Lewis acid-promoted Diels-Alder reactions. In general, cyclopentadiene or 1,3-butadiene were chosen as dienes (see, table column 4). Anthracene and other dienes, as for example (5) or (6), were examined in isolated cases as indicated in the following table. 1-Acetoxy-1,3-butadienes (5) and diene (6) were employed in natural product syntheses furnishing the desired cycloadducts as single diastereomers. 

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