Baeyer-Villiger oxidation of cyclobutanones

A systematic study of the Baeyer-Villiger oxidation of cyclobutanones was recently reported by Jeffs71). The cycloalkenes (206) reacted readily with dichloro-ketene to give the gem-dichlorocyclobutanone (205), which were reduced by Zn to the cyclobutanone (204). Baeyer-Villiger oxidation of (204) yielded the y-lactone (207) in fair yields. (Table 11)71). 

SCHEME 171. Titanium-catalyzed asymmetric Baeyer-Villiger oxidation of cyclobutanones... 

Linkers that enable the preparation of y-lactones by cleavage of hydroxy esters from insoluble supports are discussed in Section 3.5.2. Resin-bound y-lactones have been prepared by Baeyer-Villiger oxidation of cyclobutanones [39], by intramolecular addition of alkyl radicals to oximes [48], by electrophilic addition of resin-bound sele-nenyl cyanide or bromide to 3,y-unsaturated acids (Figure 9.2 [100]), and by palladium-mediated coupling of resin-bound aryl iodides with allenyl carboxylic acids (Entry 10, Table 5.7 [101]). 

Lopp, M., Paju, A., Kanger, T., Pehk, T. Asymmetric Baeyer-Villiger oxidation of cyclobutanones. Tetrahedron Lett. 1996, 37, 7583-7586. 

Stereoselective epoxidation of alkenes, desymmetrization of maso-TV-sulfonylaziri-dines, Baeyer-Villiger oxidation of cyclobutanones, Diels-Alder reactions of 1,2-dihydropyridines, and polymerization of lactides using metal complexes of chiral binaphthyl Schiff-base ligands 03CCR(242)97. 

Titanium-Catalyzed Asymmetric Baeyer-Villiger Oxidation of Cyclobutanones... 

A third variant of a metal-catalyzed enantioselective Baeyer-Villiger oxidation of cyclobutanones was reported by Lopp [30]. Up to 75% ee was achieved using the system for the epoxidation of allylic alcohols developed by Sharpless, i.e., Ti(Oi-Pr)4, chiral diethyl tartrate, and ferf-butyl hydroperoxide (Eq. 6). 

Fig. 1. IR-thermographic screening of the rare-earth catalyzed Baeyer-Villiger oxidation of cyclobutanone (27a). Well A contains cyclobutanone (27a) and dihydrogen peroxide, but no catalyst. The row blank contains dihydrogen peroxide and catalyst, but no cyclobutanone (27a).

Bohn, C., Khanh Luong, T. and Schlingloff, G. (1997). Enantioselective Metal-Catalyzed Baeyer-Villiger Oxidation of Cyclobutanones, Synlett, 10, pp. 1151-1152. 

In y-lactone synthesis through enantioselective Baeyer-Villiger oxidation, notable result was demonstrated by Mura-hashi et al. in 2002 (Scheme 8) [18]. They successfully found that planar-chiral bisflavin tethered by frans-cyclohexane-l,2diamine backbone works as an effective catalyst for enantioselective Baeyer-Villiger oxidation of cyclobutanone 19a with H2O2. Ding et al. recently reported chiral phosphoric acid 22a-catalyzed reaction with up to 88% ee of (R)-20a [19]. 

Ishihara and Uyanik [20] observed that complexes between lipophilic ion pairs such as Li[B(C6p4)4] and carboxylic acid work as Lewis acid-assisted Bronsted acid catalysts for the Baeyer-Villiger oxidation. For example, in the presence of 1 mol% of Li[B(C6p4)4] and 5 mol% of oxalic acid, fhe Baeyer-Villiger oxidation of cyclobutanone 19b gave the corresponding y-lactones 20b and 20b under mild conditions ( heme 9). 

Another method for the asymmetric version of the Baeyer-Villiger reaction was presented by Lopp and coworkers in 1996 . By employing overstoichiometric quantities of Ti(OPr-t)4/DET/TBHP (1.5 eq./1.8 eq./1.5 eq.), racemic andprochiral cyclobutanones were converted to enantiomerically enriched lactones with ee values up to 75% and moderate conversions up to 40% (Scheme 171). Bolm and Beckmann used a combination of axially chiral C2-symmetric diols of the BINOL type as ligands in the zirconium-mediated Baeyer-Villiger reaction of cyclobutanone derivatives in the presence of TBHP (or CHP) as oxidant (Scheme 172) . With the in situ formed catalysts 233a-d the regioisomeric lactones were produced with moderate asymmetric inductions (6-84%). The main drawback of this method is the need of stoichiometric amounts of zirconium catalyst. 

SYNTHESIS OF 2-(PHOSPHINOPHENYL)PYRINDINE LIGAND AND ITS APPLICATION TO PALLADIUM-CATALYZED ASYMMETRIC BAEYER-VILLIGER OXIDATION OF PROCHIRAL CYCLOBUTANONES... 

The use of a chiral hydroperoxide as oxidant in the asymmetric Baeyer-Villiger reaction was also described by Aoki and Seebach, who tested the asymmetric induction of their TADOOH hydroperoxide in this kind of reaction98. Besides epoxidation and sulfoxidation, for which they found high enantioselectivities with TADOOH (60), this oxidant is also able to induce high asymmetry in Baeyer-Villiger oxidations of racemic cyclobutanone derivatives in the presence of DBU as a base and LiCl as additive (Scheme 174). The yields and ee values (in parentheses) of ketones and lactones are given in Scheme 174 as... 

The Baeyer-Villiger oxidation of acyl-substituted cyclobutanones 1 is reported to be very slow with ordinary peracids such as 3-chloroperoxybenzoic acid24- 31 37 38 and peracetic acid.24,36 Generally, reaction times of several weeks are needed to obtain acceptable yields of acyloxycy-... 

Incorporation of substituted BINOL ligands improved the enantioselectivity of asymmetric Baeyer-Villiger oxidations of prochiral cyclobutanones with CHP and... 

Alphand V, Mazzini C et al (1998) A new microorganism for highly stereospecific Baeyer-Villiger oxidation of prochiral cyclobutanones. J Mol Catal B Enzym 5 219-221... 

Scheme 21.7 Microbial Baeyer-Villiger oxidation of prochiral cyclobutanones to access antipodal butyrolactones as a platform for the synthesis of various lignans.

An important application of metal bis(perfluorooctanesulfonyl)amides in fluorous biphasic systems is the Baeyer-Villiger oxidation. Especially Sn[N(S02C8F17)2]4 could be reused more than four times in the Baeyer-Villiger oxidation of adamantone and cyclobutanone without significant decomposition of the catalyst (Equation 4.26). It was found that there was almost no difference for the formation rate of y-butyr-olactone between the first and fourth cycles within a 1 h reaction time, which showed that there was not only no loss of the catalyst, but also no decrease in catalytic activity during the repetition [47]. 

Chiral a-methylene-y-butyrolactones An asymmetric synthesis of a-methylene- y-butyrolactones such as 7 utilizes the benzoate (2) of (1R,2S)-1, which on reaction with 1,1-dibromohexane and Zn-TiCL TMEDA forms the (Z)-enol ether 3. Thus this product reacts with dichloroketene to form the cyclobutanone (—)-4. Baeyer-Villiger oxidation of 4 followed by oxidation with chromium(Il) perchlorate provides the a-chlorobutenolide (+)-5. Hydrogenation and oxidation provides the 8-carboxy-y-butyrolactone (-) 6. The final step involves introduction of a methylene group to provide (-)-7, methylenolactocin, a natural antitumor antibiotic. 

The Pd(MeCN)2Cl2-catalysed Baeyer-Villiger oxidation of prochiral 3-substituted cyclobutanones to enantioenriched y-lactones in yields up to 99% and 81% ee has been achieved using H2O2 in THF in the presence of AgSbFg and phosphinooxazoline... 

Scheme 7.12 Baeyer-Villiger oxidations of 3-substituted cyclobutanones.

Although more than one century has gone by since its discovery in 1899, the Baeyer Villiger reaction is still far from being fully developed. In particular, there are only a few catalyst systems which afford products from the Baeyer-Villiger oxidation of 3-substituted cyclobutanones in more than 80% ee. The first example of the enantioselective Baeyer-Villiger oxidation of 3-substituted cyclobutanones catalysed by a chiral organocatalyst and 30%... 

Scheme 23.41. The asymmetric Baeyer-Villiger oxidation of 3-substituted cyclobutanones chiral cyclobutanones with H2O2 mediated by a Co(II)salen catalyst benefits greatly from the employment of micellar media instead of common organic media.

Ito K, Ishii A, Kuroda T, Katsuki T. Asymmetric Baeyer-Villiger oxidation of prochiral cyclobutanones using a chiral cationic palladium(II) 2-(phosphinophenyl)pyridine complex as catalyst. Synlett 2003 643-646. 

Petersen KS, Stoltz BM. Palladium-catalyzed, asymmetric Baeyer-Villiger oxidation of prochiral cyclobutanones with PHOX ligands. Tetrahedron 2011 67 4352- 357. 

---