Palladium-Assisted Formation of Carbon−Carbon Bonds. 6.¹ Study of the Reactivity of (o-Formylaryl)- or (o-Acetylaryl)palladium Complexes with Alkynes. Synthesis of Indenones and Indenols

The reaction of (PhCH 2 PPh 3 ) 2 [Pd(R 1 )Cl(μ-Cl)] 2 ( 1; R 1 = 6-formyl-2,3,4-trimethoxyphenyl) with PhC⋮CPh gives a 6.5:1 mixture of 4,5,6-trimethoxy-2,3-diphenylindenone ( 2 )and 4,5,6-trimethoxy-2,3-diphenyl-1 H -indenol ( 3 ). When the same reaction is carried out with MeO 2 CC⋮CCO 2 Me or with Me 3 SiC⋮CSiMe 3, the compounds 4,5,6-trimethoxy-2,3-bis(methoxycarbonyl)indenone ( 4 ) and R 1 C⋮CSiMe 3 ( 5 ) are obtained, respectively. The reactions of PhC⋮CPh with [Pd(R 1 )Cl(bpy)] ( 6; bpy = 2,2‘-bipyridine), in the presence of AgClO 4, or with [Pd(R 1 )(MeCN)(bpy)]ClO 4 ( 7 ) yield 3 and [Pd(μ-OH)(bpy)] 2 (ClO 4 ) 2 ( 8a ). If 7 reacts with PhC⋮CPh under anhydrous conditions, the indenone 2 is obtained. The complex [Pd(R 2 )(MeCN)(bpy)]ClO 4 ( 9; R 2 = 2-formyl-3,4,5-trimethoxyphenyl) reacts with PhC⋮CPh, giving 5,6,7-trimethoxy-2,3-diphenyl-1 H -indenol ( 10 ) or, under anhydrous conditions, 5,6,7-trimethoxy-2,3-diphenylindenone ( 11 ). A 1:1 mixture of both compounds is obtained by reacting [Pd(η 2 -R 2 )(μ-Cl)] 2 ( 12 ) with PhC⋮CPh. [Pd(η 2 -R 3 )(bpy)](CF 3 SO 3 ) ( 13; R 3 = 6-acetyl-2,3,4-trimethoxyphenyl) reacts with the alkynes RC⋮CR‘ (R = R‘ = Ph, 4-tolyl, CO 2 Me, Me, Et; R = Ph, R‘ = CO 2 Et, 4-nitrophenyl, 4-methoxyphenyl, Me; R = t Bu, R‘ = H, Me), yielding [Pd(μ-OH)(bpy)] 2 (CF 3 SO 3 ) 2 ( 8b ) and 1-methylindenols 14 − 24 . The catalytic reaction of [Hg(R 1 ) 2 ] with PhC⋮CPh and CuCl 2 in the presence of Q 2 [Pd 2 Cl 6 ] (1:6:2:0.05; Q = Me 4 N, PhCH 2 PPh 3 ) gives the indenol 3 in 62% yield with respect to the group R present in the mercurial compound. When a similar reaction (Q = PhCH 2 PPh 3 ) is carried out under nitrogen, the spirocyclic compound 10-formyl-6,7-dimethoxy-1,2,3,4-tetraphenylspiro[4.5]1,3,6,9-decatetraen-8-one ( 26 ) is obtained.