Enantioselective reactions rearrangements

Claisen rearrangements with 74 -, Diels-Alder reactions with 74 -, enantioselective reactions 74... 

Ramamurthy et al. have examined enantioselective and diastereoselective ODPM rearrangements of cyclohexadienone and naphthalenone derivatives within MY zeolites, where M is an alkali ion [38, 39]. For example, in Scheme 4.27, in NaY in the presence of several chiral inductors such as ephedrine, pseudoephedrine, and camphorquinone-3-oxime, an enantioselective ODPM rearrangement of 65 and 66 took place to afford 68 in 30% ee yield. In the frame of the chiral auxiliary approach, the compound 67 linked to (S)-ephedrine was irradiated within NaY to give 68 in moderate diastereoselective excess (de) (59%). Interestingly, the reaction media of KY, RbY, and CsY reverse the diastereoselectivities. The cation-dependent diastereo-meric switch has been discussed with respect to the N- or O-functional group in 67 [39]. Recently, Arumugan reported that the irradiation of naphthalenones 65 linked chiral auxiliaries (R3 = COO(—)-Ment or (S)-NHCH(Me)Ph) in Li+ or Na + Nafion resulted in chiral products ( 14% de) [40],... 

Other Enantioselective Reactions. Enantioselective epoxide elimination by chiral bases has been demonstrated. More recently, the enantioselective [2,3]-Wittig rearrangement of a 13-membered propargylic ally lie ether has been performed using the lithium amide of (f ,f )-(l) as the base for deprotonation (eq 15). For this particular substrate, THF is a better solvent than ether, although pentane produces better results in a related transformation (eq 16). In fact, a change in solvent in this type of reaction has been shown to lead to a reversal of the stereoselectivity of the transformation. ... 

Fleming, M., Rigby, J. H., Yoon, T. P., MacMillan, D. W. C. Enantioselective Claisen rearrangements Development of a first generation asymmetric acyl-Claisen reaction. Chemtracts 2001, 14, 620-624. 

In 1993, Vedejs et al. [5,6] showed that tributylphosphine is a potent catalyst for the acylation of alcohols by acetic and benzoic anhydrides as efficient as 4-(di-methylamino)pyridine DMAP [7,8]. However, the DMAP catalyst is more versatile since it presents catalytic activity in the reaction of alcohols with a larger variety of electrophiles. Due to these properties, Fu [9] realized the design and synthesis of a new family of chiral nucleophilic catalysts illustrated by the planar-chiral DMAP derivative I which is a very efficient catalyst in different enantioselective reactions such as addition of alcohols to ketenes [10], rearrangement of O-acylated azalactones [11], and kinetic resolution of secondary alcohols [12-14]. 

Butyrolactone (379) can be prepared by a highly enantioselective Claisen rearrangement starting with (S)-3-methylbutyrolactone the usefulness of this reaction has been enhanced by the development of a relatively straightforward method to transpose this initial product... 

Corey and Kania reported an enantioselective Claisen rearrangement reaction of macrocychc lactone for the synthesis of (-l-)-dollabellatrienone (56) [13], Reaction of the lactone 53 with chiral (5,5)-diazaborolidine L2BBr 54 and Barton s base (6) resulted in Claisen rearrangement to give carboxylic acid 55 in 86% yield with >98% ee (diastereos-electivity >98 2) (Scheme 7.10). In this reaction, rapid deprotonation by sterically hindered guanidine base is the key to suppress side reactions. 

More recently, they have reported an enantioselective reaction via an a-sulfi-nyl carbanion involving rearrangement to a vinyl sulfoxide [Eq. (16)] [61]. Treatment of an episulfoxide with a chiral lithium amide followed by methyla-tion yielded a methysulfinylcyclopentene with high enantioselectivity. In this reaction, the enantioselection occurs in the first deprotonation step. 

In 2008, Zhang, Ying, and co-workers reported an organocatalytic p-amination reaction of a,p-unsaturated aldehydes with nitrosobenzene catalyzed by an NHC. Specifically, the addition of NHC to a,p-unsaturated aldehyde generates a homoenolate intermediate that reacts with nitrosobenzene to afford Af-phenylisoxazolidin-5-ones, followed by an acid-catalyzed esterification and Bamberger-type rearrangement to produce Af-PMP-protected p-amino esters. A preliminary study on the enantioselective reaction of... 

Rearrangement reactions possess perfect atom economy as all the atoms of the reactant are conserved in the product. Jacobsen and eoworkers reported an attractive enantioselective Claisen rearrangement eatalysed by a guani-dinium salt, Jacobsen-G (Scheme 23.14). ... 

A recent synthesis of (+)-z5o-6-cassine makes use of enantioselective Overman rearrangement of imidate 74. Treatment of 74 with chiral cobalt oxazoline palladacycle (5)-COP-Cl vide supra) in dichloromethane gives rise to the iV-trichloroacetyl derivative 75 in good yield. This asymmetric reaction installs the absolute stereochemistry of C-6 in (+)-fso-6-cassine. ... 

Selected examples (a) J. Kaeobamrung, J. Mahatthananchai, P. Zheng, J. W. Bode, J. Am. Chem. Soc. 2010,132, 8810-8812. An enantioselective Claisen rearrangement catalyzed by N-heterocyclic carbenes. (b) Z. Q. Zhu, J. C. Xiao, Adv. Synth. Catal. 2010, 352, 2455-2458. N-heterocychc carbene-catalyzed reaction of alkynyl aldehydes with 1,3-ketoesters or 1,3-diketones. 

In 2002, Mamoka et al. reported the enantioselective Claisen rearrangement of allyl vinyl ethers 61 induced by chiral bis-organoaluminum complex 62 (Scheme 44) [77]. Reactions using mono-organoaluminum complex 63 resulted in the decrease of both chemical yields and enantiomeric excess, indicating the importance of the double coordination between carbonyl group and two aluminum centers of 62. 

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