Wagner-Meerwein asymmetric

An asymmetric [1,2]-Wagner-Meerwein shift has been achieved under Pd catalysis, allowing ring expansion of l-(alkyloxyallenyl)cyclobutanol and simple derivatives to ... 

It was mentioned above that even alkanes undergo Wagner-Meerwein rearrangements if treated with Lewis acids and a small amount of initiator. Catalytic asymmetric Wagner-Meerwein shifts have been observed. An interesting application of this reaction is the conversion of tricyclic molecules to adamantane and its derivatives. It has been found that all tricyclic alkanes containing 10 carbons are converted to adamantane by treatment with a Lewis acid, such as AICI3. If the substrate contains >10 carbons, alkyl-substituted adamantanes are produced. The lUPAC name for these reactions is Schleyer adamantization. Two examples are... 

Thus, traMi-3-alkyl-6-(phthalimido)cyclopentenes were prepared in excellent to modest yields from the corresponding tran -chloroalkene by the palladium coupling reaction [84d]. Inexpensive and efficient Pd-TMG systems, Pd(OAc)2-TMG or PdC -TMG, have been developed for the Heck reaction of an olefin with an aryl halide, in which TMG (1) acts as a ligand [84e]. In the reaction of iodobenzene with butyl acrylate the turnover numbers were up to 1000000. TMG (1) was used as a base for the palladium catalysed asymmetric Wagner-Meerwein shift of nonchiral vinylcyclopropane and cyclobutane derivatives leading to asymmetric synthesis of cyclobutanones, cyclopentenones, y-butyrolactones and 5-valerolactones [85] (Scheme 4.34). Replacement of TMG (1) with an inorganic bases such as lithium or cesium carbonate resulted in little effect. 

Scheme 4.34 Asymmetric Wagner-Meerwein shift in the presence of TMG (1)...

Trost, B.M. and Yasutaka, T. (2001) A catalytic asymmetric Wagner-Meerwein shift. Journal of the American Chemical Society, 123, 7162—7163. 

Trost BM, Xie J (2006) Palladium-catalyzed asymmetric ring expansion of allenylcyclo-butanols an asymmetric Wagner — Meerwein shift. J Am Chem Soc 128(18) 6044—6045. doi 10.1021/ja0602501... 

As a different type C-allylation, Trost reported asymmetric ring expansion involving Wagner-Meerwein shift of the allyl carbonate 173 bearing a cyclopropanol group to give the 2-vinylcyclobutanone 175 as shown by 174 in quantitative yield with 92 % ee, when Trost L-2 as a chiral ligand and TMG as a base were used. Efficient differentiation of the prochiral face of the alkene occurred [67]. 

In the year 2010, the group of Danishefsky reported the first asymmetric total synthesis of (-)-phalarine by using a Mannich reaction/Wagner-Meerwein rearrange-ment/cyclization cascade sequence (Scheme 13.9) [10], In this reaction cascade, one carbon-nitrogen bond, one carbon-carbon bond, one carbon-oxygen bond, and two new rings were formed. 

The most recent sulfide catalyst (13) made from D-camphor was reported by Huang and coworkers in 2008, which was obtained via an unexpected Wagner-Meerwein rearrangement of a dimesylate intermediate [20]. Various aromatic aldehydes can be converted into the corresponding trans 1,2-diaryl oxiranes in excellent diastereoselectivities (90 to >99% de) and high enantioselec-tivities (86-96% ee). Notably, this sulfide catalyst is also efficient for aliphatic aldehydes moderate yields (51-57%) and good enantioselectivities (71-85% ee) were observed with cyclohexane carboxaldehyde, valeraldehyde, and isovaleralde-hyde (Table 20.1). Notably, the asymmetric induction was reversed in the case of... 

---