1.3- butadienes, reaction with alkenes

Perhaps the most striking difference between conjugated and nonconjugated dienes is that conjugated dienes undergo an addition reaction with alkenes to yield substituted cyclohexene products. For example, 1,3-butadiene and 3-buten-2-one give 3-cycIohexenyl methyl ketone. 

Fluorinated cyclobutenes synthesized from the cycloaddition of fluoroalkenes with non-fluorinated alkynes (vide supra) undergo pyrolysis to give fluorinated butadienes, e.g. the pyrolysis of 3,3.4,4-tetrafluorocyclobut-l-ene gives l,1,4,4-tctrafluorobuta-l,3-diene (15) almost quantitatively. Tetrafluorodienes of this type undergo [2-F 2]-cycloaddition reactions with alkenes to give fluorinated cyclobutancs. ... 

Both 1,4- and 1,5-dienes form stable complexes with Pd. For most 1,3-dienes, such as 1,3-butadiene, reaction with Pd° compounds leads to 7r-allyl formation. These reactions are described in Section 7. The coordinated double bonds in palladium diene complexes are reactive toward attack by many nucleophiles, and the resulting chelating alkene palladium alkyls are easily isolated. Many useful reactions of dienes were discovered by Jiro Tsuji in the 1960s and 1970s. These have been recently reviewed in a historical memoir. ... 

Although methylenecyclopropanes are highly strained molecules, they are stable at ambient temperature. At elevated temperature they undergo [2 + 2]-type reaction with alkenes such as butadiene and maleic anhydride and [3 + 2] reaction with tetracyanoethylene. The latter reaction involves a trimethyl-enemethane diradical intermediate. For catalytic transformations of methylenecyclopropanes, nickel(O) and palladium(O) complexes have been used successfully. 

The TT-allyl complexes of Pd , e.g. [Pd( j -C3Hs)X]2 (X = Cl, Br, I), are very stable and more numerous than for any other metal, and neither Ni nor Pt form as many of these complexes. Indeed, the contrast between Pd and Pt is such that in reactions with alkenes, where a particular compound of Pt is likely to form an alkene complex, the corresponding compound of Pd is more likely to form a rr-allyl complex. The role of the Pd and Ni complexes as intermediates in the oligomerization of conjugated dienes (of which 1,3-butadiene, C4H6, is the most familiar) have been extensively studied, particularly by... 

The cycloaddition of alkenes is quite general and has been extended to the formation of azanickelacycles 12 by using isocyanates instead of CO2 in the reaction with alkenes or 1,3-butadienes (Eq. 6). These... 

However, in contrast to compounds with either isolated or cumulative double bonds, electrophilic addition reactions with alkenes that contain conjugated n-systems routinely produce products resulting from the interaction of both double bonds. While hydroboration appears to be an exception, with each double bond reacting separately (and the second more rapidly than the first), conjugated dienes, such as 1,3-butadiene (CH2=CH-CH=CH2), suffer addition across each double bond ( 1,2-addition ) as well as across the entire conjugated system ( 1,4-addition ). Commonly, the products ( 1,2-addition and 1,4-addition ) are formed concurrently. 

The dienoplules for reaction with butadiene can be alkenes, allenes, and alkynes. Simple alkenes like ethylene are poor dienoplules resulting in sluggish reactions. Substituted olefins, X—C=C—X, are more reactive when X and/or X are C=C, Ar, COOR, COOH, COH, COR, COCl, CN,... 

Although hexafluoro-l,3-butadiene is better known for its [2+2] reactions, its Diels-Alder reactions, particularly with electron-deficient alkenes such as acrylonitrile and perfluoropropene, are not unknown [9] The first report of a Diels-Alder reaction is with an acetylenic dienophile Although the major product of Us reaction with phenylacetylene is its [2+2] adduct, a 3 5% yield of products of a Diels-Alder reaction is also observed [123] (equation 103)... 

A simple approach for the formation of 2-substituted 3,4-dihydro-2H-pyrans, which are useful precursors for natural products such as optically active carbohydrates, is the catalytic enantioselective cycloaddition reaction of a,/ -unsaturated carbonyl compounds with electron-rich alkenes. This is an inverse electron-demand cycloaddition reaction which is controlled by a dominant interaction between the LUMO of the 1-oxa-1,3-butadiene and the HOMO of the alkene (Scheme 4.2, right). This is usually a concerted non-synchronous reaction with retention of the configuration of the die-nophile and results in normally high regioselectivity, which in the presence of Lewis acids is improved and, furthermore, also increases the reaction rate. 

The Diels-Alder reaction,is a cycloaddition reaction of a conjugated diene with a double or triple bond (the dienophile) it is one of the most important reactions in organic chemistry. For instance an electron-rich diene 1 reacts with an electron-poor dienophile 2 (e.g. an alkene bearing an electron-withdrawing substituent Z) to yield the unsaturated six-membered ring product 3. An illustrative example is the reaction of butadiene 1 with maleic anhydride 4 ... 

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. 

Reaction of a,/MJnsaturated Fischer Carbene Complexes with Alkenes, Butadienes, Enamines, and Imines... 

The mixtures are particularly dangerous with alkenes, cycloalkenes and dienes. Accidents have been reported with propene, butenes, isobutylenes, 1-hexene, butadiene and cyclopentadiene. However, the reaction below is not thought to be dangerous if one operates at a temperature of 30°C and under two bar. 

Absolute rates for the addition of the methyl radical and the trifluoromethyl radical to dienes and a number of smaller alkenes have been collected by Tedder (Table l)3. Comparison of the rate data for the apolai4 methyl radical and the electrophilic trifluoromethyl radical clearly show the electron-rich nature of butadiene in comparison to ethylene or propene. This is also borne out by several studies, in which relative rates have been determined for the reaction of small alkyl radicals with alkenes. An extensive list of relative rates for the reaction of the trifluoromethyl radical has been measured by Pearson and Szwarc5,6. Relative rates have been obtained in these studies by competition with hydrogen... 

Electron-rich 3-methoxy-4-trimethylsilyl-l,2-butadiene (22) reacted with several electron-poor alkenes in the presence of diethylaluminum chloride to afford methylene cyclobutanes 23. Reactions with alkynes were performed in the presence of methylalu-minum bis(2,4,6-tri-t-butylphenoxide) (equation 7)16. 

Copper-catalyzed monoaddition of hydrogen cyanide to conjugated alkenes proceeded very conveniently with 1,3-butadiene, but not with its methyl-substituted derivatives. The most efficient catalytic system consisted of cupric bromide associated to trichloroacetic acid, in acetonitrile at 79 °C. Under these conditions, 1,3-butadiene was converted mainly to (Z )-l-cyano-2-butene, in 68% yield. A few percents of (Z)-l-cyano-2-butene and 3-cyano-1-butene (3% and 4%, respectively) were also observed. Polymerization of the olefinic products was almost absent. The very high regioselectivity in favor of 1,4-addition of hydrogen cyanide contrasted markedly with the very low regioselectivity of acetic acid addition (vide supra). Methyl substituents on 1,3-butadiene decreased significantly the efficiency of the reaction. With isoprene and piperylene, the mononitrile yields were reduced... 

The transition metal catalysed addition of HCN to alkenes is potentially a very useful reaction in organic synthesis and it certainly would have been more widely applied in the laboratory if its attraction were not largely offset by the toxicity of HCN. Industrially the difficulties can be minimised to an acceptable level and we are not aware of major accidents. DuPont has commercialised the addition of HCN to butadiene for the production of adiponitrile [ADN, NC(CH2)4CN], a precursor to 1,6-hexanediamine, one of the components of 6,6-nylon and polyurethanes (after reaction with diisocyanates). The details of the hydrocyanation process have not been released, but a substantial amount of related basic chemistry has been published. The development of the ligand parameters % and 0 by Tolman formed part of the basic studies carried out in the Du Pont labs related to the ADN process [1],... 

The addition of a hydrogen halide, such as HBr, is an important addition reaction for alkenes often seen in Organic Chemistry 1. However, conjugated dienes may behave differently. An example is the reaction of HBr with 1,3-butadiene as illustrated in Figure 4-11. 

The use of lithium amides to metalate the a-position of the N-substituent of imines generates 2-azaallyl anions, typically stabilized by two or three aryl groups (Scheme 11.2) (48-62), a process pioneered by Kauffmann in 1970 (49). Although these reactive anionic species may be regarded as N-lithiated azomethine ylides if the lithium metal is covalently bonded to the imine nitrogen, they have consistently been discussed as 2-azaallyl anions. Their cyclization reactions are characterized by their enhanced reactivity toward relatively unactivated alkenes such as ethene, styrenes, stilbenes, acenaphtylene, 1,3-butadienes, diphenylacetylene, and related derivatives. Accordingly, these cycloaddition reactions are called anionic [3+2] cycloadditions. Reactions with the electron-poor alkenes are rare (54,57). Such reactivity makes a striking contrast with that of N-metalated azomethine ylides, which will be discussed below (Section 11.1.4). 

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