Allylic chlorides, from dienes

If the side chain with the nucleophile is situated in the 1-position of the conjugated diene, a palladium-catalyzed spirocyclization occurs. In this case stereoselective oxa-spirocyclizations were obtained from the diene alcohols 59 and 60 (equation 23 -25)58. The reaction worked well for the formation of a tetrahydrofuran and tetrahydropyran in the spirocyclization. In the absence of chloride ions 59 gave high yields of the acetoxy oxaspirocyclic compound 61 via a 1,4-anti addition across the diene (equation 23). In the presence of stoichiometric amounts of LiCl a 1,4-syn oxychlorination took place and allylic chloride 62 was obtained (equation 24). Under chloride-free conditions, cyclohep-tadiene alcohol 60 afforded oxaspirocyclic acetate 63 (equation 25). 

The allyl chloride 353 is prepared from diprenyl ether (352), and its Pd-catalysed 1,4-elimination in the presence of AcONa affords the conjugated diene 354. Citral (355) is obtained by the consecutive Claisen and Cope rerrangements of 354 [168],... 

Abstraction of chloride from a vinylpalladium complex by silver acetate has been reported,45 as well as halide abstraction by silver triflate from arylpalladium halides.46 More interestingly in the context of creating C-C bonds, silver perchlorate was able to promote the reaction of (r -aryl)palladium bromide with dienes. Silver-promoted bromide abstraction led to the formation of (r 1-r 2-enyl)palladium complexes, which evolved further through the regioselective formation of a C-C bond between the aryl group and the former diene. Reactions with nonconjugated dienes suggested that the reaction proceeds via carbometallation of the less crowded double bond. Isomerization and (3 elimination led to a (ri3-allyl)palladium complex (Scheme 10.26).47... 

Palladium coordinates to one face of the diene promoting intramolecular attack by the alcohol on the opposite face. The resulting <7-alkyl palladium can form a 71-allyl complex with the palladium on the lower face simply by sliding along to interact with the double bond. Nucleophilic attack of chloride from the lithium salt then proceeds in the usual way on the face opposite palladium. The overall addition to the diene is therefore cis. 

Therefore, the isomerization reaction was also performed starting from the a-substituted enol ether 119 (Scheme 52). By using the tandem allylic C-H activation-elimination reactions, Z-120c is initially formed and by a transmetalation reaction into organocopper with a stoichiometric amount of CuCI/ 2LiCl, followed by heating at +50 °C for 1 h and reaction with allyl chloride, the resulting ( , )-diene 122 is obtained with an isomeric ratio of 90 10 but in a low 40% yield as described in Scheme 52. 

The (S)-lactone acid 1, obtained from L-glutamic acid by nitrous acid deamination, was converted to the acid chloride, then treated with excess diazomethane followed by hydrogen iodide to yield the keto-lactone 2. Amidation occurred quantitatively to give the partially racemized amide 3, which was purified by repeated recrystallizations. The vicinal diol resulting from reaction with excess methylmagnesium iodide was protected as the acetonide 4. An isomeric mixture of olefins (Z , 26 74) was obtained from the subsequent Wittig reaction. Reduction followed by separation on silver nitrate coated silica gel gave the (Z)-and ( )-alcohols in 20% (6) and 61% (5) yield, respectively. Conversion of the (S)-( )-alcohol (5) to the chloride then afforded the thioether (7) on reaction with sodium phenylsulfide. The thio ether anion was formed by treatment with n-butyllithium. Alkylation with the allylic chloride" (8), followed by removal of sulfur, then yielded the diene 9, which was converted in several steps to (/ ) (-t-)-10,11 -epoxy famesol. 

PdCE-catalyzed addition reaction of allyl chloride to alkynes is explained by chloropalladation of a triple bond, followed by insertion of the double bond of allyl chloride to generate 43. No jr-allyl complex is formed from allyl chloride and PdCl2. The final step is elimination of /3-Cl to afford 1-chloro-1,4-diene 44 with regeneration of Pd(ll) [37]. As another example, the Pd(0)-catalyzed Heck reaction of vinyl acetate affords stilbene in this reaction, the primary product is /3-phenylvinyl acetate (45), which reacts again with iodobenzene, and the last step is elimination of /S-OAc to give stilbene. At the same time, Pd(II) is generated, which is reduced to Pd(0) in situ [38]. However, elimination of /3-heteroatoms is not always faster than that of j8-H. For example, the Heck reaction of allyl alcohol with iodobenzene proceeds by preferential elimination of /3-H from the insertion product 46 to afford aldehyde 47, and no elimination of /3-OH from the same carbon occurs to give the alkene 48 [39,40]. 

The ease with which nucleophiles add to alkenes and alkynes coordinated to Pd(II) combined with the tendency of Pd to form rr-allyl complexes accounts for the limited number of Pd(II)-alkene, Pd(II)-diene, or Pd(II)-alkyne complexes. Indeed, as detailed in the next section, depending on the conditions or their structural features, alkenes, dienes, and alkynes often lead to the formation of 7r-allylpalladium complexes instead of rf or rf rr-complexes. This is particularly true in the case of alkenes bearing hydrogens a to the double bond, 1,3-dienes, such as 1,3-butadiene, and alkynes of low steric hindrance, hi marked contrast, Pd(l,5-hexadiene)Cl2 is obtained from the reaction of Cl2Pd(PhCN)2 with allyl chloride. ... 

Access to the vinyl alcohol 4 (Figure 4a) is straightforward, and when elimination of the tertiary hydroxyl group was attempted by treatment with thionyl chloride in pyridine at -40°C, a mixture of three compounds was obtained. Along with the expected product 1, an isomeric diene, 5, was found in a 1 1 ratio. This compound arose from the elimination of the H-4 proton. The third component of this mixture was proved to be the rearranged allylic chloride 6 (8) formed via an SnF reaction of the intermediate allylic chlorosulphite (9). 

The allylic chloride moiety is the cure site for polychloroprene pol5uners (Fig. 2). The reaction of the labile allylic chlorides with bifimctional nucleophiles, metal oxides, or thioureas covalently joins interpolymer chains into a polymer network. The pol5uner cross-link density is proportional to the concentration of allylic chlorides on the polymer backbone. Thus mechanical goods with high modulus are made from polymers of high allylic chloride concentration. On the other hand, high levels of allylic chlorides decrease the thermal stability of polychloroprene polymers per mechanism described for thermal degradation of imsaturated diene polymer (56,57)... 

Some of the specific unsaturated substrates suffering from the above shortcomings, which also leverage many commercial applications as well as various synthetic transformations useful to research, are allyl chloride, allyl alcohol derivatives, and a number of compounds with a electron-withdrawing group at the allylic position. Also handicapped are many 1,3-dienes, and other dienes where the desirable terminal olefinic product either cannot be obtained (butadiene, for instance), or suffers partial isomerization to the internal olefin which then is not useful for the targeted application. 

Alkynes can be dimerized in a head-to-tail fashion to unsymmetrical 1,3-dienes (42) in excellent yield via vinylmercurials. 1,4-Dienes are obtained from the same intermediates and excess allyl chloride, both reactions being catalysed by transition-metal systems. 

In a similar manner, three-component coupling of allyl chlorides or acetates with 1-alkynes and alkynyltins in the presence of a nickel catalyst prepared in situ from Ni(acac)2 and DIBALH provides a convenient regio- and stereoselective synthesis of 3,6-dien-l-ynes [231,232], It is interesting to note that no phosphine ligands are required in these reactions. A Jt-allylnickel intermediate is proposed. 

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. 

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