Synthesis reactions butadiene

The preparation of 2-chlorothiopyrylium salts can be accomplished by a two-component synthesis. Reaction of /ru/ij-rra/i5-1,4-diphenyl-1,3-butadiene with excess thiophosgene gives 2-chloro-3,6-diphenylthiopyry-lium chloride 102 in high yield (Scheme 7) (67ZC227). The reaction probably consists in a Diels-Alder cycloaddition, followed by elimination of HCl and hydride abstraction. When the reaction was carried out with l-phenyl-3-methyl-l,3-butadiene, the 3,5-disubstituted thiopyrylium 103 was isolated without evidence of the 4,6-disubstituted regioisomer (84AP938). 

This type of reaction is now of major industrial importance because it constitutes a straiglitforward synthesis of nitriles. Wlien it is applied to a diolefm, such as butadiene, it leads to the formation of dinitriles, which are precursors of valuable monomers for the preparation of polymers (butadiene leads to adipo-nilrile. a nylon-b, fvprecursor). Du Font developed the first commercial process using butadiene and HCN for adiponitrile synthesis from butadiene, but this process does nut proceed through a hydrocyanation reaction it is. in fact, a copper-catalyzed halogenation reaction followed by a cyanaikm reaction (tquaiion (16)) of the chlorinated intermediate (Fquation (17)). 

The application of hypervalent iodine(III) mediated and catalyzed amination of hydrocarbon substrates has developed into a useful tool for organic synthesis. Reactions comprise direct amination of sp-, sp -, and sp -hybridized C-H bonds and numerous oxidative transformations of alkenes, butadienes, and allenes. Some of these methods have been developed directly in the form of catalytic transformations, which adds to underline the synthetic potential of the field. Where applicable, the possibility for enantioselective transformations has been demonstrated for some cases. One can be optimistic that hypervalent iodine chemistry is able to complement existing methodology for oxidative amination reactions in a practical manner over the next few years. 

Nickel(O) forms a n-complex with three butadiene molecules at low temperature. This complex rearranges spontaneously at 0 °C to afford a bisallylic system, from which a large number of interesting olefins can be obtained. The scheme given below and the example of the synthesis of the odorous compound muscone (R. Baker, 1972, 1974 A.P. Kozikowski, 1976) indicate the variability of such rearrangements (P. Heimbach, 1970). Nowadays many rather complicated cycloolefins are synthesized on a large scale by such reactions and should be kept in mind as possible starting materials, e.g. after ozonolysis. 

Direct addition of ammonia to olefmic bonds would be an attractive method for amine synthesis, if it could be carried out smoothly. Like water, ammonia reacts with butadiene only under particular reaction conditions. Almost no reaction takes place with pure ammonia in organic solvents. The presence of water accelerates the reaction considerably. The reaction of aqueous ammonia (28%) with butadiene in MeCN in the presence orPd(OAc)i and PhjP at 80 C for 10 h gives tri-2,7-octadienylamine (47) as the main product, accompanied by a small amount of di-2,7-octadienylamine (46)[46,47], Isomeric branched... 

Another example is the du Pont process for the production of adiponitrile. Tetrakisarylphosphitenickel(0) compounds are used to affect the hydrocyanation of butadiene. A multistage reaction results in the synthesis of dinitrile, which is ultimately used in the commercial manufacture of nylon-6,6 (144-149). 

A second synthesis of cobyric acid (14) involves photochemical ring closure of an A—D secocorrinoid. Thus, the Diels-Alder reaction between butadiene and /n j -3-methyl-4-oxopentenoic acid was used as starting point for all four ring A—D synthons (15—18). These were combined in the order B + C — BC + D — BCD + A — ABCD. The resultant cadmium complex (19) was photocyclized in buffered acetic acid to give the metal-free corrinoid (20). A number of steps were involved in converting this material to cobyric acid (14). 

Nckel catalyzed steroeselective synthesis ol cis and trans methyl vinykryclopentanes Irom telemerization of butadiene Cyclization (ene reaction) of unsaturated ellyl Qrignard reagents... 

Cycloaddition involves the combination of two molecules in such a way that a new ring is formed. The principles of conservation of orbital symmetry also apply to concerted cycloaddition reactions and to the reverse, concerted fragmentation of one molecule into two or more smaller components (cycloreversion). The most important cycloaddition reaction from the point of view of synthesis is the Diels-Alder reaction. This reaction has been the object of extensive theoretical and mechanistic study, as well as synthetic application. The Diels-Alder reaction is the addition of an alkene to a diene to form a cyclohexene. It is called a [47t + 27c]-cycloaddition reaction because four tc electrons from the diene and the two n electrons from the alkene (which is called the dienophile) are directly involved in the bonding change. For most systems, the reactivity pattern, regioselectivity, and stereoselectivity are consistent with describing the reaction as a concerted process. In particular, the reaction is a stereospecific syn (suprafacial) addition with respect to both the alkene and the diene. This stereospecificity has been demonstrated with many substituted dienes and alkenes and also holds for the simplest possible example of the reaction, that of ethylene with butadiene ... 

Node and co-workers have found that the Diels-Alder reaction of nitroalkenes v/ith 1-methoxy-3-trimethylsilyloxy-l,3-butadiene (Danishefsky s dienesi exhibit abnormal exo-se-lecdvity Electrostadc repulsion between the nitro and the silyloxy group of the diene induces this abnormal exc-selecdvity (Tq 8 10 This selecdve reacdon has been used for the asymmetric synthesis of various naniral products as shovm in Scheme 8 6... 

Scheme 8 presents the sequence of reactions that led to the synthesis of the B-ring of vitamin B12 by the Eschenmoser group. An important virtue of the Diels-Alder reaction is that it is a stereospecific process wherein relative stereochemical relationships present in the diene and/or the dienophile are preserved throughout the course of the reaction.8 Thus, when the doubly activated dienophile 12 (Scheme 8) is exposed to butadiene 11 in the presence of stannic chloride, a stereospecific reaction takes place to give compound 27 in racemic form. As expected, the trans relationship between... 

In the synthesis of the taxol skeleton, two successive applications of the reaction on a masked equivalent for 2,3-bis(bromomethyl)-l,3-butadiene are the key steps59. 

A further extension of the MIMIRC reaction is seen in the synthesis of enantiomerically pure cyclohexanones. A successful diastereoselective MIMIRC reaction with 2-(rer/-butyldimethylsi-lyloxy)-4-phenyl-l,3-butadiene and an optically pure (Z)-y-alkoxy-substituted enone was performed using catalytic amounts (5 mol%) of triphenylmethyl perchlorate at — 78 ,C 360,408 (for a further example see Section 1.5.2.4.4.1.). 

A similar elimination in which the tin is attacked by fluoride anions (cf. the reaction of silanes with F ) has been used179 to synthesize terminal methylene compounds as in equation (75). An analogous reaction sequence using a trimethylsilyl group in place of the trialkyltin group has been published by Hsiao and Shechter180 as part of a synthesis of substituted 1,3-butadienes. 

The synthesis of 2-chloro-2,3,3-trifluorocyclobutyl acetate illustrates a general method of preparing cyclobutanes by heating chlorotrifluoroethylene, tetrafluoroethylene, and other highly fluorinated ethylenes with alkenes. The reaction has recently been reviewed.11 Chlorotrifluoroethylene has been shown to form cyclobutanes in this way with acrylonitrile,6 vinylidene chloride,3 phenylacetylene,7 and methyl propiolate.3 A far greater number of cyclobutanes have been prepared from tetrafluoroethylene and alkenes 4,11 when tetrafluoroethylene is used, care must be exercised because of the danger of explosion. The fluorinated cyclobutanes can be converted to a variety of cyclobutanes, cyclobutenes, and butadienes. 

However, exo-selective Diels-Alder reactions are found when a,/J-unsatu-rated exocyclic carbene complexes are used as dienophiles. The fixed s-cis conformation of the vinylcarbene moiety of the complex seems to be responsible for the exo selectivity observed in this reaction. Moreover, the reaction of optically active carbene complexes with 2-morpholino- 1,3-butadienes allows the asymmetric synthesis of spiro compounds [99] (Scheme 53). 

Synthesis of functionalized aryloxy 1,3-butadienes and their transformation to dienyl ethers via Diels-Alder cycloaddition reactions [136]... 

More functionalized 5,6-dihydro-2H-pyran-derivatives 71 and 72 have been prepared [26] by cycloaddition of 1 -methoxy-3-trialkylsilyloxy-1,3-butadienes 69 with t-butylglyoxylate (70) (Scheme 5.6). Whereas thermal reactions did not occur in good yields because of the decomposition of the cycloadducts, application of pressure (10 kbar) allowed milder conditions to be used, which markedly improved the reaction yields. The use of high pressure also gives preferentially en Jo-adduct allowing a stereocontrolled synthesis of a variety of substituted 5,6-dihydro-2H-pyran-derivatives, which are difficult to prepare by other procedures. 

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