L-Methoxy-2,7-octadiene

Palladium complexes generated from the sulfonated ligand 5 (Table 2 R=Me, n=0,l,2) were also used to catalyse the telomerization of 1,3-butadiene with water108 and from the aminophosphines 83 (Table 5 R=Ph R =H,Me R"=Me,iPr n=2,3) with MeOH to give l-methoxy-2,7-octadiene in selectivities up to 78% at conversions ranging from 52 to 80%.232 Pd/83 (R=Ph R =H,Me R"=Me,iPr n=2,3) catalysts are more active but less selective in the latter reaction compared to their tppts counterparts.232 9... 

More importantly the telomers 133 and 134 are formed by the reaction of pronucleophiles (NuH), incorporating the Nu group [51,52,53]. The reaction can be explained by the amphiphilic nature of bis-it-allylpalladium 68. The first step is the nucleophilic attack of the amphiphilic bis-it-allylpalladium 68 to NuH (or protonation) as shown by 130 to generate n-allylpalladium 131=132, and their electrophilic attacks as shown by 131 and 132 afford 133 and 134 [53a]. The reaction, carried out in deuterated MeOD, affords l-methoxy-2,7-octadiene (135), deuterated at carbon 6 [54]. Pd(Ph3P)4 serves as the catalyst. Most conveniently, Pd(OAc)2 and Ph3P are used as the catalyst precursor. In this case, Pd(OAc)2 is reduced in situ to Pd(0), which is an active species. 

The reaction of butadiene with methanol leads to the formation of the telomers l-methoxy-2,7-octadiene (trans- and cis-), 3-methoxy-l,7-octadiene and the dimers 1,3,7-octatriene and 4-vinylcyclohexene (as minor products). Using palladium(II) acetate with either PPh3 or TPPMS in a biphasic system with ionic liquid leads to an inactive system when [C2mim]+ and [C4mim]+... 

Telomerizations have been among the first reactions tested under biphasic conditions [45, 190], starting with butadiene and methanol on Pd/TPPMS catalysts and yielding l-methoxy-2,7-octadiene. The telomerization in the presence of water as reactant (hydrodimerization cf Scheme 1) has been commercialized [15, 31, 42-44]. These biphasic developments of the Kuraray Corporation yield 1-octanol or 1,9-nonanediol, respectively (cf [15, 31, 42 4, 86, 133, 137, 244 e] and Section 2.3.5). Similar developments (but without technical realization) have been described by BASF [134], Mitsubishi [135], and Shell [136], and others [215 d, 242, 268]. The telomerization of butadiene and ammonia may also be biphasic [243]. 

An active catalytic species in the dimerization reaction is Pd(0) complex, which forms the bis-7r-allylpalladium complex 3, The formation of 1,3,7-octa-triene (7) is understood by the elimination of/5-hydrogen from the intermediate complex 1 to give 4 and its reductive elimination. In telomer formation, a nucleophile reacts with butadiene to form the dimeric telomers in which the nucleophile is introduced mainly at the terminal position to form the 1-substituted 2,7-octadiene 5. As a minor product, the isomeric 3-substituted 1,7-octadiene 6 is formed[13,14]. The dimerization carried out in MeOD produces l-methoxy-6-deuterio-2,7-octadiene (10) as a main product 15]. This result suggests that the telomers are formed by the 1,6- and 3,6-additions of MeO and D to the intermediate complexes I and 2. 

The reaction of isoprene with MeOH catalyzed by Pd(acac)2 and Ph3P is not regioselective, giving a mixture of isomers[37]. However, l-methoxy-2,6-dimethyl-2,7-octadiene (35), the head-to-tail dimer, was obtained in 80% yield, accompanied by the tail-to-tail dimer (15%) using 7r-allylpalladium chloride and BU3P. On heating, 35 was converted into 2.6-dimethyl-1,3,7-octatriene (36) by an elimination reaction[38]. 

Asymmetric telomerization of isoprene and methanol by using chiral phosphines, such as menthyldiphenylphosphine, gave an optical yield of 17.6%. The telomerization of methanol and isoprene using w-allylpalla-dium chloride and PBu3 in the presence of sodium methoxide in a mixed solvent of methanol and isopropyl alcohol at room temperature for 2 days produced l-methoxy-2,6-dimethyl-2,7-octadiene (89) (80%) and 1-meth-oxy-2,7-dimethyl-2,7-octadiene (91) (15%) (91). After 2 days, the reaction mixture was heated at 80°C for 8 hours, and 2,6-dimethyl-l,3,7-octatriene (88) (75%) and 2,7-dimethyl-1,3,7-octatriene (85) (14%) were obtained. Also, NiCl2(Bu3P)2 was used as a cocatalyst for the formation of 88. 

Butadiene trans, frans- 1,8-Dime thoxy-2,6-octadie tie (13%), Irani-l,6-dimethoxy-2,7-octadiene (13%), 3,6-di-methoxy-l,7-octadiene (13%), dimethoxydodeca- ... 

Precursors for the synthesis of ( + )- and (—)-citronellol (2) are enantioselectively prepared via palladium-catalyzed dimerization of isoprene in the presence of methanol which gives ( )-8-methoxy-3,7-dimelhyl-l,6-octadiene (1) in up to 93 % yield with optical purities of up to 35% when 71-allylpalladium chloride dimer, with the addition of optically active phosphane ligands derived from menthol, is used as catalyst31,32. 

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