1-Acetoxy-1,3-butadiene, reaction with

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... 

Table 5.1 High pressure Diels-Alder reactions of (E)-l-acetoxy- (18a) and (E)-l-methoxy butadiene (18b) with acrylic and crotonic dienophiles...

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. 

The 5,6-double bond in activated pyrimidines such as 2-acylamino-6-acetyl-4(lH)-pyrimidinones (427) undergo Diels-Alder reactions to yield on heating with l-acetoxy-3-methylbutadiene (428) hydroquinazolines (429). The yields are modest, but the regiochemistry is clean. With 1,3-butadiene and with isoprene the cycloadducts were formed in low yields (83JOC3627). 

Diels-Alder reactions.1 A key step in a synthesis of 4-demethoxydaunomy-cinone (5) involves a regioselective Diels-Alder reaction of anthracene-1,4,9,10-tetrone (2) with (1) to give the desired adduct (3) in 79% yield. A similar reaction with 2-acetoxy-1,3-butadiene affords only a 58% yield of the corresponding adduct. The product (rather unstable) is aromatized and hydrolyzed to give 4 in high yield. 

Photo-[4+2] reactions of the dienone steroid 105 illustrates interesting regio-, stereo-, and site selectivities (Sch. 24) [75-78]. Reaction with 1-acetoxy-1,3-diene 106 gives trans adduct 107 in good yield, epimeric at the acetate. The trans cycloaddition was attributed to a triplet pathway rather than a twisted enone intermediate [75]. Reaction with 2,3-dimethyl-1,3-butadiene 108 leads to four [4+2] adducts, with reaction at both alkenes groups of the dienone. Note that the products of reaction at the y,5-alkene are both cis. 

Easily prepared from glycols, enones have been investigated as dienophiles. They react with butadiene under Lewis acid catalysis to form chiral cyclohexenes used in the synthesis of compactin analogs [353]. Levoglucosenone has been used in a Diels-Alder reaction with acetoxy-butadiene to construct a part of the indole alkaloid reserpine [354], and in synthetic studies toward tetrodotoxin [355]. Analogs of the anthracycline rhodomycinone have been similarly prepared [356]. [4 + 2]-Cycloaddition of the same enone with silyloxydiene allowed the creation of the fused ring system present in actinobolin [357]. 

It is well established that steric effects hinder the Cope rearrangement of divinylcyclopropanes. An interesting example of this steric effect is seen in the reaction of 33 with cis- and trans-l-acetoxy-butadiene (Scheme 13). ° The reaction of 33 with trans-1-acetoxy-l, 3-butadiene leads cleanly to the [3+4] annulation product 34 in 67% yield. In contrast, the product from the reaction of 33 with c/j-l-ace-toxy- 1,3-butadiene is the cw-divinylcyclopropane 35 (80% yield), and high temperatures (220 °C) are required to convert 35 to the [3+4] annulation product 36. The effect of alkene geometry on the stereochemistry and the rate of reaction is readily explained by considering the boat transition state for the Cope rearrangement of divinylcyclo-propanes (structure 37). A trans diene substituent (Y) would generate a trans product (34), whereas a cis substituent (X) would lead to a cis... 

It is possible to prepare 1-acetoxy-4-chloro-2-alkenes from conjugated dienes with high selectivity. In the presence of stoichiometric amounts of LiOAc and LiCl, l-acetoxy-4-chloro-2-hutene (358) is obtained from butadiene[307], and cw-l-acetoxy-4-chloro-2-cyclohexene (360) is obtained from 1.3-cyclohexa-diene with 99% selectivity[308]. Neither the 1.4-dichloride nor 1.4-diacetate is formed. Good stereocontrol is also observed with acyclic diene.s[309]. The chloride and acetoxy groups have different reactivities. The Pd-catalyzed selective displacement of the chloride in 358 with diethylamine gives 359 without attacking allylic acetate, and the chloride in 360 is displaced with malonate with retention of the stereochemistry to give 361, while the uncatalyzed reaction affords the inversion product 362. 

Uncatalyzed Diels-Alder reactions between l-(trimethysiloxy)- or 1-acetoxy-l,3-butadiene and sugar-derived nitroalkenes having D-galacto or D-manno configurations proceed with complete regioselectivity. Diastereofacial selectivity is also complete with the D-galacto dieno-phile, whereas it is only moderate with the D-manno (Eq. 8.30).51... 

Pd2+ salts are useful reagents for oxidation reactions of olefins. Formation of acetaldehyde from ethylene is the typical example. Another reaction is the formation of vinyl acetate by the reaction of ethylene with acetic acid (16, 17). The reaction of acetic acid with butadiene in the presence of PdCl2 and disodium hydrogen phosphate to give butadienyl acetate was briefly reported by Stem and Spector (110). However, 1-acetoxy-2-butene (49) and 3-acetoxy-l-butene (50) were obtained by Ishii and co-workers (111) by simple 1,2- and 1,4-additions using PdCl2/CuCl2 in acetic acid-water (9 1). 

When the reactions of 494 with some dienes were carried out under thermal conditions, the adducts were obtained metal-free. This suggested the possibility of effecting these transformations using a catalytic amount of an appropriate Cr(0) source. Rigby and colleagues showed that the reaction between cycloheptatriene 511 and 1-acetoxy-1,3-butadiene (341) can be catalyzed by employing a catalytic amount of 513 (equation 149). The yield of 512 was 36% in this instance, whereas a yield of 20% was obtained when a catalytic amount (10 mol%) of 494 was used as the catalyst305,308. 

The first studies of chlorine addition to the simplest diene, 1,3-butadiene, carried out in solvents of various polarity, showed58 that the reaction always led to mixtures of 1,2- and 1,4-addition products, in ratios almost independent of the solvent polarity. Furthermore, the addition of CI2 in acetic acid gave, besides the 1,2- and 1,4-dichlorides, 3-acetoxy-4-chloro-l-butene and l-acetoxy-4-chloro-2-butene arising from solvent incorporation (equation 27). By comparison of these data with those related to Br2 addition... 

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. " ... 

Reaction of PhZnCl with 3-acetoxy-3-methyl-1-butyne (116) gives l-phenyl-3-methyl-1,2-butadiene (119) in high yield [28-30]. The reaction can be explained by transmetallation of the allenylpalladium intermediate 117 with PhZnCl to generate the allenyl(phenyl)palladium intermediate 118, followed by reductive elimination to afford 119. 

Palladium(II)-promoted oxidative 1,4-difunctionalization of conjugated dienes with various nucleophiles is a useful reaction [98], The reaction is stoichiometric with respect to Pd(II) salts, but it can be made catalytic by use of Pd(0) reoxidants. 1,4-Difunctionalization with the same or different nucleophiles has wide synthetic application. The oxidative diacetoxylation of butadiene with Pd(OAc)2 proceeds by acetoxypalladation to generate the 7i-allylpalladium 136, which is attacked by acetoxy anion as the nucleophile, and (E)-, 4-diacctoxy-2-butcnc (137) is formed with 3,4-diacetoxy-1-butene (138) as the minor product. The commercial process for 1,4-diacetoxy-2-butene (137) by the reaction of butadiene, AcOH and O2 has been developed using a supported Pd catalyst containing Te. 1,4-Butanediol (139) and THF are produced commercially from l,4-diacetoxy-2-butene (137) [99]. 

A new synthetic method for steroids has been developed using a butadiene dimer (66) as a building block and the palladium-catalyzed oxidation as the key reaction. 3-Acetoxy-l,7-octadiene (66), prepared by the palladium-catalyzed reaction of butadiene with acetic acid, is hydrolyzed and oxidized to... 

A new synthetic method for steroids has been developed using a butadiene dimer (66) as a building block and the palladium-catalyzed oxidation as the key reaction.3-Acetoxy-l,7-octadiene (66), prepared by the palladium-catalyzed reaction of butadiene with acetic acid, is hydrolyzed and oxidized to l,7-octadien-3-one (67) in high yield. The enone (67) is a very useful reagent for bisanellation because its termiiud double bond can be regarded as a masked ketone which can be readily unmasked by the palladium catalyst to form the l,S-diketone (68) after Michael addition at the enone moiety of (67 Scheme 20). Thus, the enone (67) is the cheapest and most readily available bisanellation reagent, permitting a simple total synthesis of steroids. 

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