Tert-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. 

Besides the reaetions with allenes, alkynes, and ketimines deseribed above, the C—Rh speeies generated from the aromatic C—H bond activation was also found capable to insert smoothly into ketones. In this eontext, the groups of Cramer and of Murakami independently developed a similar strategy to achieve this transformation. Typically, tert-cyclobutanols were utilized as the standard substrates in this strategy. As depieted in the proposed catalytic cycle (Scheme 5.50), the Rh catalyst first coordinates to the substituted cyclobutanol and the resulting intermediate undergoes facile... 

Scheme 5.51 Formation of indanols and indanones by p-carbon elimination of tert-cyclobutanol.

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. 

Rh-catalyzed stereoselective isomerization of tert-cyclobutanols into chiral indanoles 2.2.1 Overview... 

Seiser, T. Roth, O. A. Cramer, N. Enantioselective Synthesis of Indanols from tert-Cyclobutanols Using a Rhodium-Catalyzed C-C/C-H Activation Sequence. Angew. Chem., Int. Ed. 2009,48,6320-6323. 

Scheme 5 -Carbon eliminations from tert-cyclobutanolates...

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

Later on, the reactivity was extended to electron-rich alkoxyallenyl tert-cyclobutanols [62, 63], With this substrate class, hydropalladation of the allene generates the required a -aUylpalladium intermediate 114 to trigger the 1,2-shift (Scheme 24). Again, ring expanded cyclopentanones 115 were obtained in high yields, enantioselectivity, and diastereoselectivity with L13. A critical point of the initial hydropalladation is careful pH control. 

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... 

Seiser T, Roth OA, Cramer N (2009) Enantioselective synthesis of indanols from tert-cyclobutanols using a rhodium-catalyzed C-C/C-H activatirai sequence. Angew Chem Int Ed 48(34) 6320-6323. doi 10.1002/anie.200903189... 

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. 

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