PALLADIUM-ASSISTED FORMATION OF CARBON-CARBON BONDS .3. STUDY OF REACTIONS OF -6-ACETYLPHENYL-C,O))BIS(MU-CHLORO)DIPALLADIUM(II) WITH SYMMETRICAL AND UNSYMMETRICAL INTERNAL ALKYNES - A STOICHIOMETRIC ROUTE TO HIGHLY FUNCTIONALIZED SPIROCYCLIC AND BENZOFULVENE COMPOUNDS - ISOLATION OF A PI-ALLYLIC PALLADIUM INTERMEDIATE - X-RAY STRUCTURE OF 3,4-TETRAPHENYLSPIRO[4.5]1,3,6,9-DECATETRAEN-8-ONE

The reactions of -6-acetylphenyl-C,O)}bis(mu-chloro)dipalladium(II) (I ) with different internal alkynes ArC=CR, Ar = aryl and R = aryl or CO (2)R', result in the selective formation of spirocyclic organic compou nds. Thus, 1 reacts with diphenyl- or bis(4-tolyl)acetylene giving 3,4 -tetraphenylspiro[4.5]1,3,6,9-decatetraen-8-one (2) or trakis(4-tolyl) spiro[4.5]1,3,6,9-decatetraen-8-one (3), respectively. Among unsymmetr ical alkynes, ethyl 2-phenylpropiolate gives the head-to-tail isomer x y-1,3-diphenylspiro[4.5]1,3,6,9-decatetraen-8-one (4) as the only isom er whereas methyl 2-phenylpropiolate gives xy-1,3-diphenylspiro[4.5]1, 3,6,9-decatetraen-8-one (5a) as the major isomer and a small amount of a head-to-head or tail-to-tail isomer (5b), the ratio 5a/5b being 5/1 . When these reactions are carried out with unsymmetrical diarylalkyne s, Ar = Ph, R = 4-nitrophenyl or 4-methoxyphenyl, a moderate or no reg ioselectivity toward the head-to-tail spiro product is observed. The m olar ratios of this isomer to the head-to-head and to the tail-to-tail isomers are, respectively, 4/1/1 or 2/1/1. When one of the sustituent s is an alkyl group, for example R = Me, the benzofulvene 5,6,7-trimet hoxy-3-methyl-2-phenyl- 1-methylene-1H-indene (2-PhBzf) (9) is obtaine d along with the mixture of spiro compounds (head-to-tail (8a)/head-to -head or tail-to-tail (8b) = 7/1; 8/9 = 8/1.5). Dialkylacetylenes reac t with 1 giving benzofulvenes (Bzf). Thus, 1 reacts with dimethyl- or tert-butylmethylacetylene giving 2-MeBzf (10) or 2-(t)BuBzf (11). The reaction of 1 with diethylacetylene gives both isomers E- and trimetho xy-3-methyl-2-ethyll-ethylidene-1H-indene, (E)-12 and (Z)-12 (2.6/1). In the reaction of 1 with diphenylacetylene, an organopalladium interm ediate can be isolated, which reacts with 2,2'-bipyridine and thallium (I) trifluoromethylsulfonate giving the (pi-allyl)palladium complex, , 6-decatrien-8-enyl}(2,2'-bipyridine)palladium(II) trifluoromethylsulfo nate (13), the structure of which has previously been reported. Reduct ion of 2 with Na[BH4] gives 3,4-tetraphenylspiro[4.5]1,3,6,9-decatetra en-8-one (14), the structure of which has been determined by diffracti on at -130 degrees C. It crystallizes in P2(1)2(1)2(1) with a = 10.635 (3) Angstrom, b = 13.199(4) Angstrom, c = 20.643(7) Angstrom and R = 0 .063). The structure consists of two ring systems, 2,3,4,5-tetraphenyl cyclopenta-2,4-diene and thoxy-6-(1-hydroxyethyl)-cyclohexa-2,5-dien-4 -one, with a common spiro carbon atom.