Palladium cyclobutanols

Matsumura, S. Maeda, Y. Nishimura, T. Uemura, S. Palladium-catalyzed asymmetric arylation, vinylation, and allenylation of tert-cyclobutanols via enantioselective C—C bond cleavage./. Am. Chem. Soc. 2003, 125, 8862-8869. 

Zucco, M. Le Bideau, F. Malacria, M. Palladium-catalyzed intramolecular cyclization of vinyloxirane. Regioselective formation of cyclobutanol derivatives. Tetrahedron Lett. 

An exception involves the passage of hot alcohol vapors over thorium oxide at 350-450°C, under which conditions Hofmann s mle is followed, and the mechanism is probably different. Cyclobutanol derivatives can be opened in the presence of a palladium catalyst. 2-Phenylbicyclo[3.2.0]octan-2-ol, for example, reacted with a catalytic amount of palladium acetate in the presence of pyridine and oxygen to give phenyl methylenecyclohexane ketone. ... 

In the arylative ring opening of 3-substituted cyclobutanols, enantioselective cleavage of the C-C bond has been achieved by using a palladium catalyst with a chiral ligand [33-35]. Particularly, the use of the chiral ferrocene-containing N,P-bidentate ligand shown in Eq. 17 leads to excellent enantioselectivity. 

A palladium-catalysed tandem semipinacol rearrangement/direct arylation reaction using a-aryl isopropenyl-t-cyclobutanols has been reported (Scheme 138). ... 

The Pd-catalyzed reaction of tert-cyclobutanols in the presence of pyridine gives the ring-opening products. For example, 7-vinylbicyclo[4.2.0]octan-7-ol (17) was converted to l-(2-methylenecyclohexane-l-yl)-2-propen-l-one (18) in 56% yield upon tfeat-ment with Pd(OAc)2, pyridine, and MS3A under O2 atmosphere (Scheme 25). The reaction seems to involve /3-carbon cleavage (bond a breaking) from the palladium alkox-ide intermediate. 

Scheme 26.15 Phosphcaic acid effect in the activation of cyclobutanols toward palladium-catalyzed migratory ring expansion.

Phosphoric acids have also been applied as the chiral inductor in combination with palladium (II) catalysts in the migratory ring expansion of cyclobutanols to yield spirocyclicindenes. This transformation is believed to proceed via enantioselective aUylic C-H activation followed by semi-pinacol ring expansion to the vicinal 7r-allylpalladium intermediate (Scheme 26.15) [84],... 

Scheme 9 Palladium-catalyzed -carbon elimination from tcrt-cyclobutanols and subsequent arylative trapping...

Scheme 23 Enantioselective palladium-catalyzed ring expansion of /ert-cyclopropanols and tert-cyclobutanols...

Nishimura T, Ohe K, Uemura S (1999) Palladium(n)-catalyzed oxidative ring cleavage of tert-cyclobutanols under oxygtai atmosphere. J Am Chem Soc 121(11) 2645—2646. doi 10.1021/ ja984259h... 

Nishimura T, Uanura S (1999) Palladium-catalyzed arylation of tert-cyclobutanols with aryl bromide via C-C bond cleavage new approach fin the y-arylated ketones. J Am Chem Soc 121 (47) 11010-11011. doi 10.1021/ja993023q... 

Nishimura T, Matsumura S, Maeda Y, Uemura S (2002) Palladium-catalysed asymmetric arylation of tert-cyclobutanols via enantioselective C-C txmd cleavage. Chem Commun 7 (1) 50-51. doi 10.1039/bl07736h... 

Matsumura S, Maeda Y, Nishimura T, Utanura S (2003) Palladium-catalyzed asymmetric arylation, vinylation, and allcaiylation of teat-cyclobutanols via enantioselective C-C bond cleavage. J Am Chem Soc 125(29) 8862-8869. doi 10.1021/ja035293l... 

Transition metal alkoxides of tert-cyclobutanols undergo ring opening by P-carbon elimination to generate ketones that are metalated at the y-position these can be utilized in many functionalization reactions. Palladium, rhodium, and nickel have been the most studied metals in these transformations. Useful transition metal cyclobutanolates are generated from either cyclobutanones or cyclobutanols. 

Palladium(0)-catalyzed asymmetric arylation of tert-cyclobutanol 33 with bromobenzene, involving enantioselective C-C bond cleavage, furnished the chiral y-arylated ketone 34 (Scheme 3.13) [24]. Good enantioselectivity was observed when a chiral ferrocenyl P,N-ligand was used. y-Alkenylated and y-allenylated ketones were also obtained by asymmetric ring opening. 

An intramolecular variant of palladium-catalyzed arylative ring opening of cyclobutanols was developed, in which P-carbon elimination occurred at the more congested quaternary carbon to produce five-membered carbocycles (Scheme 3.14) [25]. 

The organopalladium species in turn can be cross-coupled, for example with aryl halides. Since 3-substituted cyclobutanols are prochiral, an asymmetric ring-opening would deliver chiral, nonracemic palladium species. This has been investigated by Uemura (Scheme 5-148). ... 

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