The allylic groups of ethers and esters exchange with a variety of active hydrogen compounds in the presence of palladium catalysts.IN the degradation of octa-Z,7-dienyl phenyl ether to phenol and octa-1,3,7-triene with a palladium catalyst,l Smutny observed the formation of a small amount of 2and 4-(octa-2,7-dienyl)phenol,2 which is obviously not formed via a normal or abnormal Claisen rearrangement of the ether.We find that the octadienyl group of octa-2,7-dienyl phenyl ether exchanges with a variety of active-hydrogen compounds in the presence of palladium catalysts, and further research has led to the finding that the allylic compounds (I) react with active-hydrogen compounds to give allylic derivatives of the active-hydrogen compounds R10-CH2CH = CHR2
Active methylene compounds, such as acetylacetone and ethyl acetoacetate, reacted with 1,3-butadiene in the presence of palladium-diphosphine complex catalysts to yield two 1 : 1 adducts, 1 and 2. Primary and secondary amines also afforded two 1 : 1 adducts, 10 and 11. Isoprene, 1,3-pentadiene, and 2,4-hexadiene also reacted with the active methylene compounds and the amines in a manner similar to that of 1,3-butadiene. The most effective and easily available catalyst is the combination of PdBr2(Ph2PCH2CH2PPh2)2 and sodium phenoxide.
The allylic compounds (I), R1–O–R (R=allylic groups, R1=Ph, Me, PhCH2, MeCO), react with active-hydrogen compounds such as phenols, alcohols, carboxylic acids, primary and secondary amines and active methylene compounds, to give allylic derivatives of the active-hydrogen compounds by an intermolecular exchange of the allylic groups of I with the atom to which the active hydrogens are bonded in the presence of palladium catalysts. Allyl and substituted-allyl ethers are more reactive than the corresponding carboxylates. In the reactions of methyl and benzyl ethers, it is necessary to add phenol to obtain the exchange products in fairly good yields. Bis(triphenylphosphine) palladium chloride plus sodium phenoxide, palladium acetate plus triphenylphosphine, and zerovalent palladium complexes such as tetrakis (triphenylphosphine) palladium and (maleic anhydride)bis(triphenylphosphine)palladium are effective catalysts.
In the presence of palladium and platinum catalysts, 1,3-dienes react with active methylene and methyne compounds such as 0-keto esters, ß diketones, dialkyl malonates, -formyl ketones and esters, -cyano and «-nitro esters, and ethyl phenylsulfonylacetate to form corresponding 2,7-alkadienyl derivatives. In the palladium-catalyzed reactions of active methylene compounds with 1,3-butadiene, 1:2 adducts 1 and 1:4 adducts 2 are obtained as main products, and small amounts of branched 1:2 adduct 3 are isolated as by-products.Addition of isoprene to active methylene compounds gives 2,7-dimethyl-2,7-octadienyl derivatives 4 and 5, derived from tail-to-tail dimerization of isoprene, almost selectively. In contrast to the addition of isoprene, the reaction of 1,3-pentadiene affords a head-to-tail adduct 6. In the platinum-catalyzed reaction of 1,3-butadiene with active methylene compounds, a ratio of the branched 1:2 adduct 3 to all the adducts is larger than that observed in the palladium-catalyzed reaction, and 1:1 adduct and 1:3 adduct are isolated as by-products besides 1, 2, and 3. A reaction intermediate 7 involving a four-coordinated palladium system derived from the tertiary phosphine complex of palladium(0) is postulated.
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