2-methoxy-1,3-butadiene carbonate

Cycloaddition reactions of (E)-l-acetoxybutadiene (18a) and (E)-l-methoxy-butadiene (18b) with the acrylic and crotonic dienophiles 19 were studied under high pressure conditions [9] (Table 5.1). Whereas the reactions of 18a with acrylic dienophiles regioselectively and stereoselectively afforded only ortho-enJo-adducts 20 in fair to good yields, those with crotonic dienophiles did not work. Similar results were obtained in the reactions with diene 18b. The loss of reactivity of the crotonic dienophiles has been ascribed to the combination of steric and electronic effects due to the methyl group at the )S-carbon of the olefinic double bond. 

When butadiene is treated with PdCU the l-chloromethyl-7r-allylpalladium complex 336 (X = Cl) is formed by the chloropalladation. In the presence of nucleophiles, the substituted 7r-methallylpalladium complex 336 (X = nucleophile) is formed(296-299]. In this way, the nucleophile can be introduced at the terminal carbon of conjugated diene systems. For example, a methoxy group is introduced at the terminal carbon of 3,7-dimethyl-I,3,6-octatriene to give 337 as expected, whereas myrcene (338) is converted into the tr-allyl complex 339 after the cyclization[288]. 

The reaction of 2,3-butadienyl acetate (843) with soft carbon nucleophiles such as dimethyl malonate gives dimethyl 2,3-butadienylmalonate (844)[520]. On the other hand, the reaction of the 2,3-butadienyl phosphate 845 with hard carbon nucleophiles such as Mg and Zn reagents affords the 2-allcyl-1,3-butadiene 846[520,521]. The 3-methoxy-1,3-butadiene 848 is obtained by the reaction of the 2-methoxy-2,3-butadienyl carbonate 847 with organozinc reagent. 

The Diels-Alder reaction of 2-methoxy-l,3-butadiene and acrylonitrile can give either the 1,3- or the 1,4-disubstituted product. Use Spartan View to examine the HOMO surface of 2-mcthoxy-1,3-butadiene. Which terminal diene carbon has the larger HOMO lobe and is thus a better electron donor Next, simultaneously display the density surface and LUMO surface of acrylonitrile, and look at how the LUMO extends beyond the density surface. Which dienophile carbon is a better electron acceptor Which of the two products should form most rapidly ... 

Acid-catalyzed hydrolysis of isobutylene oxide (8) is >750 times faster than that of ethylene oxide (6), and > 99% of the glycol product is from addition of solvent at the tertiary carbon.23 These results are consistent with a mechanism in which there is significant positive charge on the tertiary carbon at the transition state, as discussed in the previous section. Butadiene monoepoxide (10) is slightly less reactive than isobutylene oxide,36 and its acid-catalyzed hydrolysis can potentially proceed via a resonance-stabilized allyl cation (Scheme 6). However, the acid-catalyzed hydrolysis of 10 yields 96% of 3-buten-l,2-diol (15) and only 4% of 2-butene-1,4-diol (16),36 and the acid-catalyzed methanolysis of 10 is reported to yield only 2-methoxy-3-buten-l-ol.37 An A-2 mechanism proceeding via transition state 17 may account for the observation that 1,2-diol 15 is the predominant product from acid-catalyzed hydrolysis of 10. The minor yield of the 1,4-diol 16 may be formed from reaction of... 

In the latter case, some (118) was also formed. The reaction of 3-thiolen-2-one with 1,3-cyclopentadiene proceeded rapidly at room temperature in the presence of boron trifluoride etherate, to give (119). An exception was the reaction with 1-methoxy-3-C(trimethyls ilyl)oxy]butadiene, which only led to silyl transfer, giving 2-(trimethylsiloxy)thiophen and 4-methoxy-but-3-en-2-one.6 The reaction between the ambient anion of the 5-methyl-2-hydroxy-thiophen system with carbon disulphide and methyl iodide gave (121) in 36% yield, in addition to the expected product (120). Tfie structure of the latter compound was proven by X-ray crystallography, and a reaction path for its formation was suggested. The... 

DIELS-ALDER REACTIONS l,3-Bis(trimethylsilyIoxy)-l,3-butadiene. trans, rnms-1,4-Diacetoxybutadiene. 1,2-Dicyanocyclobulene. Ethyl /fans-1,3-butadiene-I-carbonate. Furane. 2-(2-MethoxyFallylidene-l,3-dithiane. 2-Methoxy-3-phenyIthiobuta-l,3-diene. l-Methoxy-3-trimcthylsilyloxy-l,3-butadiene. Sulfur dioxide. 1-Trimethylsily 1-1,3-butadiene. 2-Trimethylsilyloxy-l, 3-butadiene. 

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