Arylation cyclobutanols

Simiraly, alkynones undergo arylative cyclization with arylboronic acids in the presence of a rhodium catalyst (Equation (49)).400 When acetylenic /3-keto esters are employed as shown in Equation (50), arylative cyclization (formation of cyclobutanols) and subsequent, facile acid-catalyzed bond cleavage take place to give <5-keto esters.401 Ring expansions of cyclic [3-keto esters are also possible according to this reaction. 

Ketones with the general structure R — C(O) —C(R R2) — C(R3,R ) — CH(R5,R6) (R = aryl or alkyl) undergo intramolecular H-abstraction on excitation in competition with cleavage of one of the C(O) — C bonds.1 The resulting 1,4-diradical then either closes to a cyclobutanol or undergoes cleavage of the central C2 — C3 bond with formation of an enol and an alkene. 

The same mode of migration is found if the rc-bond needed for rearrangement is part of an aryl ring in the 2-position. Usually only the substituted C3 of cyclobutanones (Table 5)71 74,140 or cyclobutanols (Table 6)75 migrates on treatment with trifluoroaeetic acid,73 methanesulfonic acid,71 trifluoromethanesulfonie acid, 140/ -toluenesulfonic acid,74 phosphorus pentoxide,71-74 and tin(IV) chloride,72 generally with diethyl ether or benzene as the solvent. 

Keywords czv-9-dccalyl aryl ketone, Norrish type II photochemistry, cyclopropanol, cyclobutanol, cyclopentanol... 

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. 

Pioneering work on the photochemical diastereocontrol in zeolite supercages was reported by Turro and coworkers in 1991 [48]. They investigated the diastereoselective photodecarbonylation of 2,4-diphenyl-3-pentanone (DPP) adsorbed in various cation-exchanged X and Y zeolites to find that the diastereo-selectivity of d9l- over mestf-2,3-diphenylbutane increases in the order LiX NaX < LiY NaY < KY. In 1996, Ramamurthy and coworkers reported the first example of photochemical asymmetric induction in chirally modified zeolites [49], where they employed the Norrish/Yang type II reaction of cis-4-tert-butyl-cyclohexyl aryl ketones to the corresponding cyclobutanols. Since then, a variety of asymmetric photoreactions in zeolite supercages have been reported as reviewed below. 

Ramamurthy, Scheffer and coworkers and other investigators reported the enantiodifferentiating Norrish/Yang photocyclization [49-53] of aryl cis-4-tert-buty -cyclohexyl ketones 1 to cyclobutanols 2 (Scheme 1) in chirally modified zeolite supercages [49]. 

Highly enantioselective Norrish/Yang photocyclization of cw-4-terf-butyl-1-benzoylcyclohexane 47 was also achieved in salt crystals using chiral amines like R)- + )-l-phenylethylamine or (—)-norephedrine [61,63]. Furthermore, cis-9-decalyl aryl ketones 49 in their salt crystals with chiral amines such as (/ )-( + )-bomyl amine or ( )-( — )-1 -phenylethylamine underwent highly regio-, dia-stereo- and enantioselective Norrish/Yang photocyclizations to give the cyclobutanol 50 alone in > 98% ee [64]. 

A similar reaction has been described for the preparation of thioethers with aryl-and alkylthiotrimethyl silanes.Ring-closure occurs with co-bromo-1,2-epoxyalkanes on the action of magnesium and lithium in the presence of Cul. By this means, cyclobutanol, cyclopentanol, and cyclohexanol can be prepared. (e.g. Eq. 294). 

Type II hydrogen abstraction by the keto group from the adjacent aryl methyl group to give the biradical (60) from which both products (61) and (62) are formed. The reaction is solvent dependent. In cyclohexane solvent only the cyclobutanols (61) are formed, but in methanol a mixture of (61) and the new diketone (62) are obtained in a ratio which is dependent upon steric factors. The photochemically induced proton transfer in 3-methyl-6-hydroxy-m-phthalic acid has been reported. ... 

Carbonyl compounds. Allylic alcohols are oxidized under ethylene with Pd(OAc)2 as catalyst. A more conventional hydrogen acceptor is molecular oxygen in such oxidation. Under such conditions, cyclobutanols that are gem-vinylated or arylated are cleaved (further transformations are also possible). ... 

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. 

Other than cyclobutanols, the four-membered ring of myrtenal also undergoes the arylative ring opening to afford a monocyclic product with a moderate... 

The l-(l-alkynyl)cyclobutanol 120 was expanded by Pd-catalyzed reaction with aryl- and alkenyl halides to produce the 2-(2-arylidene)cyclopentanones 123. The reaction can be understood formally by carbopalladation to give 121, and migration of an electron-rich carbon to Pd to form the palladacyclohexanone 122, and the cyclopentanone 123 is obtained by reductive elimination of 122 (see Chapter 3.8.2) [40],... 

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

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