Treatment of 15hexaa'ien-3-01s in acetic acid by Pd(0) [Pd(PPh&] led to l-methyl-1,3-cyclopentadienes. Cyclization is improved by the presence of catalytic amount of mfluoroacetic acid. Mechanism is discussedfrom the observed results with deuterated alcohols.
The reaction of palladium complexes with C-nucleophiles is an attractive synthetic tool.t-9 In particular, the intramolecular olefin allylation of olefntic allylacetates A or B constitutes a ring closure leading to 1-methylene-2vinylcycloalkanes or 1,2-divinylcycloalkanes.2~
(G or (GGAc
These cyclizations provide a variety of five-(six-) membered carbocyclic systems from olefinic allylacetates with n = 3 or 4, and, to our knowledge, no report concerns the case n = 1, corresponding to 1,5hexadien-3-01 derivatives. The expected palladium-catalyzed intramolecular metallo-ene reactions should lead to the formation of attractive cyclopropane derivatives or resulting products: $-wdb ='d$)-'$fH-JOr 4 +Pd"+H+ X In this context, we studied the cyclization of some 15hexadien-3-01s lo easily obtained by ally1 Grignard reagent addition to unsaturated ketones. t1 First, we have observed that allylpulegols la, b treated in acetic acid solution by Pd(PPh& (3 mole %, 80 93, 4 h.) cyclized in bicyclo[4.3.0]nona-1(6),7dienes 2a,b along with trienes 3a,b and 4. The relative proportions are variable, the main product being 2a,b. To increase the proportion of cyclopentadienes, we operated to reflux (CA 4 h), the only hydrocarbon isolated was 2a.b in 70-75 56 yield. Clearly, the trienes 3a.b are precursors of 2a,b: the ueatment of 3b by Pd(PPh3)4 under reflux of acetic acid led to 2 b : I ,3,6-heptatrienes could be cyclized into I -methyl-l ,3-cyclopentadienes.