Carbon−Carbon Bond Formation in Regio- and Stereoselective Palladium-Catalyzed Cyclization of Allene-Substituted Conjugated Dienes

Abstract

Regio- and stereoselective palladium-catalyzed reactions of allene-substituted 1,3-dienes 1 in acetic acid at room temperature lead to cyclization with formation of a carbon-carbon bond between the middle carbon of the allene and the terminal carbon of the 1,3-diene. Two different types of reactions, both that constitute 1,4-carboacetoxylations of the 1,3-diene, have been developed. In one of the reactions, Pd(II) catalyzes the oxidation of 1 to bicyclic compounds 2, and in the other, Pd(0) catalyzes the transformation of 1 to bicyclic compounds 3. The products 2 are useful for further synthetic transformations and undergo Diels-Alder reactions with dienophiles to give polycyclic ring systems.

Allenes as Carbon Nucleophiles in Intramolecular Attack on (π‐1,3‐Diene)palladium Complexes: Evidence for trans Carbopalladation of the 1,3‐Diene

“…For a comparison with our previous results, [9] complexes 3 a and 3 b were transformed to their isoprenyl analogues 6 a and 6 b, respectively, by treatment with silica gel (Scheme 4). Treatment of complexes 3 a and 3 b with silica in CH 2 Cl 2 at room temperature overnight afforded complexes 6 a and 6 b, respectively.…”

“…[6,8] We recently reported on an intramolecular palladium(ii)-catalyzed reaction of allenic conjugated dienes involving carbon ± carbon bond formation between the allene and diene moieties. [9] Several mechanisms were proposed as likely pathways and one of the mechanisms considered involves trans nucleophilic attack by the allene on a (p-diene)palladium(ii) complex. Such trans attack by p-nucleophiles on coordinated carbon ± carbon double bonds is rare and the only established example is allylsilane attack on a (p-diene)palladium complex.…”

Development of Useful Reactions Involving Tandem Cyclizations Based on the Novel Reactivities of Allenic Compounds

“…73,74) Palladium(II)-catalyzed oxidative cyclization of allene-substituted alkenes and palladium(0)-catalyzed cyclization of allenes bearing an allyl ester moiety were reported by Bäckvall. 75,76) Oh and co-workers reported cyclization of allenynes in the presence of a palladium catalyst and organic acid. 77,78) However, palladium(0)-catalyzed tandem cyclization of an allene that contains an additional multiple bond has scarcely been investigated.…”

Control of Selectivity in Palladium‐Catalyzed Oxidative Carbocyclization/Borylation of Allenynes

“…In ongoing investigations our research group has been studying oxidative Pd II -catalyzed carbocyclizations of various unsaturated molecules 12–15. Recently we accomplished the carbocyclization/arylation of allenynes with arylboronic acids 13b.…”

“…The allene attack on Pd II complex A through allylic C–H bond cleavage12, 13a–d would give B and subsequent alkyne insertion would generate intermediate C . Transmetalation of C with B 2 pin 2 and reductive elimination would form product 4 .…”