Palladium-catalyzed controlled carbopalladation of benzyne

2-Trimethylsilylphenyl trifluoromethanesulfonate la, a benzyne precursor, r eacted with the allylic chlorides 2a-f in the presence of CsF (2.0 equiv) a nd Pd-2(dba)(3). CHCl3 (2.5 mol %)-dppf (5 mol %) in a 1:1 mixed solvent of CH3CN and THF to produce the phenanthrene derivatives 3 along with their m inor regioisomers 4 in good yields (i) and the reaction of la with 2a and t he internal alkynes 15a,c-e afforded the naphthalene derivatives 16 in mode rate yields (ii). The reaction of benzyne precursor la with the alkynes 15a -c,f-h in the presence of Pd(OAc)(2) (5 mol %)-(o-tolyl)(3)P (5 mol %) cata lyst and CsF (2.0 equiv) in CH3CN gave the phenanthrene derivatives 17 (iii ), whereas the reaction of la with the alkynes 15a,b,i in the presence of t he same catalysts and CsF in CH3CN-toluene gave the indene derivatives 18 i n good yields (iv). Detailed mechanistic investigation revealed that the fo rmer two reactions i and ii proceed through carbopalladation to free benzyn e, while the latter two reactions iii and iv proceed through the nonfree be nzyne mechanism, in which the initial step of the catalytic cycle begins wi th Pd(0) insertion to the Ar-OTf bond of 1.