Heck Reaction of Aryl Bromides with Pent-4-en-2-ol, 2-Phenylpent-4-en-2-ol, or Hept-6-en-3-ol Catalysed by a Palladium-Tetraphosphine Complex

Abstract

The tetraphosphine cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane in combination with [Pd(η 3 -C 3 H 5 )Cl] 2 affords a very efficient catalyst for the Heck reaction of aryl bromides with pent-4-en-2-ol, 2-phenylpent-4-en-2-ol, or hept-6-en-3-ol. With pent-4-en-2-ol or hept-6-en-3-ol, the selectivity in favour of the formation of the 5-arylpentan-2-one or 7-arylheptan-3-one derivatives, respectively, depends on the substituents on the aryl bromide and on the base. Sterically congested and electron-rich aryl bromides gave selectively the linear ketones by migration of the double bond. With electron-poor aryl bromides, the formation of large amounts of (E)-arylalk-1-enol derivatives or side products was observed in some cases. Similar reactions rates were observed with electron-poor and electron-rich aryl bromides. Several reactions can be performed with as little as 0.01% catalyst. A wide variety of substituents, such as methoxy, dimethylamino, fluoro, trifluoromethyl, acetyl, benzoyl, formyl, carboxy, or cyano groups, on the aryl bromides are tolerated. The coupling of very sterically congested aryl bromides, such as 9-bromoanthracene or 2-bromo-1,3,5-triisopropylbenzene, also proceeds in good yields. Heck reaction with 2-phenylpent-4-en-2-ol gave the expected (E)-5-aryl-2-phenylpent-4-en-2-ol derivatives in high turnover numbers (TONs) and high selectivities in most cases. However, with some electron-poor aryl bromides the selective formation of 1-arylprop-1-ene derivatives resulting from a C-C bond cleavage was observed.