Isoprene palladium-catalyzed reactions

Palladium-catalyzed reaction of isoprene with thiophenol in the presence of CO gave, depending on the solvent, either a thiocarbonylation product (16a) or a product in which a 1,4-addition of sulfur and a hydrogen had occurred (16b) [31]. The reaction was optimized for the formation of the thiocarbonylation product (in CH2CI2) to give 1,4-addition products in good yields. 

J. Tsuji, Adv. Organomet. Chem., 1979, 17, 141-193. Palladium-Catalyzed Reactions of Butadiene and Isoprene. 

Palladium-catalyzed addition of phenylsulfinic acid to butadiene and isoprene gave mainly 1,2-addition products. From butadiene, a 4 1 ratio of 1,2- to 1,4-addition product was obtained in high yield [Eq.(ll)] [27]. It was later shown that the 1,2-addition product is the kinetic product and that prolonged reaction time increased the amount of 1,4-addition product [27b]. 

A further noteworthy side reaction of palladium-catalyzed methylenecyclopropane cycloadditions is the isomerization of 2-(n-alkyl) methylenecyclopropanes to isoprene-type dienes, and subsequent reaction of the latter with electron-deficient alkenes to form cyclohexenes in a Diels — Alder reaction, rather than providing [3 + 2]-addition products. 

Hydrocarbons. The reaction of isoprene with toluene, ethylbenzene, or isopropylbenzene is catalyzed by sodium or potassium (72). The reactions are carried out at 125°C in a pressure autoclave by adding the isoprene slowly to the alkylarene in which the alkali metal is dispersed along with a trace quantity of 0-chlorotoluene which is used as a chain initiator. The products are chiefly monopentenylated in the side chain, and no information can be obtained on whether the addition is 1,4- or 1,2- since under these conditions the double bond migrates. The alkene products subsequently are reduced to alkanes by hydrogenation using 5% palladium on charcoal as catalyst. 

Trost has reported enhanced enantioselectivity in the desymmetrization of mero-biscarbamates in the presence of triethylamine. Under these conditions, high yields (>80%) and enantiomeric excesses (93-99% ee) are obtained. This methodology has been applied to the synthesis of (—)-swainsonine. a-Amino esters have been used as nucleophiles in the reaction with acyclic allylic esters and isoprene monoepoxide, providing access to diastereoselective N-alkylated a-amino esters. By employing the feature ligand, asymmetric palladium(0)-catalyzed cychzation of 2-(tosylamino)phenol with ( -l,4-bis[(methoxycarbonyl)oxy]but-2-ene provides 2-vinylbenzomorpholine in 79% ee. A number of alternative diphosphine ligands were studied and found to be inferior. 

The use of PhS02Na in the palladium(0)-catalyzed (Pd(PPh3)4) reaction of isoprene in DMF afforded the 1,4-addition product exclusively in 94% yield [29]. The regioisomer obtained was the l-phenylsulfonyl-3-methylbut-2-ene. 

Palladium-phosphine complexes catalyze the similar 1,4-bis-silylation with the activated disilanes. In the presence of palladium-PPh3 complexes, fluoro-[55] and chloro-disilanes [56] provide 1,4-products 59 in good yields with high stereoselectivity giving Z-alkenes (Eq. 27). In the reaction of fluorinated disilane with isoprene, a minor amount of 1 2 adduct 60, which arises from regioselective... 

Simple 1,3-dienes such as 1,3-butadiene, isoprene, and related compounds undergo efficient metal-catalyzed oligomerization. Under palladium catalysis, diene dimerization is the most common oligomerization reaction observed. Four modes of dimerization have been reported (Scheme 1) (i) [2 + 2] cycloaddition to afford 1,2-divinylcyclobutane (1) (ii) [4 -I- 2] cycloaddition to afford 4-vinylcyclohexene (2) (iii) [4 + 4] cycloaddition to afford 1,4-cyclooctadiene (3) and (iv) linear dimerization to afford 1,3,7-octatriene (4). 

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