162395-63-3Relevant articles and documents
Palladium-catalyzed cyclization of ω-haloallenes. A new general route to common, medium, and large ring compounds via cyclic carbopalladation
Ma, Shengming,Negishi, Ei-Ichi
, p. 6345 - 6354 (2007/10/02)
A series of ω-haloallenes (4-32) as well as related ω-haloalkenes (41-45) were prepared through the application of known procedures. Their cyclization in the presence of a catalytic amount of Cl2Pd(PPh3)2, a base, e.g., K2CO3, and other appropriate reagents was investigated mostly under two sets of conditions (conditions I and II). The results summarized in Table 1 reveal the following: (1) The Pd-catalyzed cyclization reaction of ω-haloallenes gives the desired five- through twelve-membered and twenty-membered ring products in respectable yields. (2) The use of the dilute solution technique and n-Bu4NCl is advantageous in the synthesis of eight-membered and larger rings. (3) Formation of a carbon-carbon bond uniformly takes place at the central carbon of an allene. (4) The corresponding reaction of ω-haloalkenes fails to give eight- and nine-membered rings and displays an intriguing endo - exo cyclization mode vs ring size profile. (5) The eight-membered ring products were exclusively Z, and the eleven-, twelve-, and twenty-membered ring products were E. The stereochemistry of the nine- and ten-membered rings depends on other factors as well. The putative allylpalladium intermediates can be trapped with external nucleophiles, such as malonate esters, organostannanes, phenols, and amines, to give the corresponding derivatives. The results support the oxidative addition - carbopalladation mechanism leading to the formation of allylpalladium intermediates. The results also indicate that the extents of the actual cyclization process itself may be considerably higher than indicated by the yields of the dehydropalladation products and that some undesirable side reactions, such as double bond isomerization, can be circumvented through trapping with nucleophiles.
