Diastereoselectivity Claisen-Ireland rearrangements

Claisen rearrangement of glycolates. Two laboratories 2 have reported that allylic glycolate esters undergo Claisen-Ireland rearrangement (6, 276-277) with useful diastereoselectivity. This rearrangement was used in a synthesis of 1, the aggregation pheromone of the European elm bark beetle.1... 

Fig. 11.46. Claisen-Ireland rearrangements with simple diastereoselectivity.

Alkenylsilanes having a (methoxy)acetoxy group at the allylic position derived from optically active allylic alcohols undergo the Claisen-Ireland rearrangement to give highly functionalized allylsilanes in a highly diastereoselective manner (Scheme 3-54).t 2J... 

Silyl-substituted ally methoxyacetate 1 undergoes the Claisen-Ireland rearrangement to diastereoselectively give optically active allylic silane 2 as exemplified by Scheme 5.1. The resulting silane is employed for asymmetric addition to both aliphatic and aromatic acetals 3a and 3b in the presence of MejSiOTf, giving rise to homoallylic ethers 4a and 4b, respectively, with high diastereo- and enantioselec-tivities [4]. The whole sequence of reactions is an example of 1,4- and 1,5-remote... 

In 1986, Kraus [129], Gilbert [130] and VanMiddlesworth [131] all reported application of the Ireland-Claisen rearrangement in syntheses of the trichothecenes trichodiene and bazzanene. In each case the diastereoselectivity of the rearrangement was minimal as a result of a lack of stereoselectivity in the enolization of the ester. The Kraus synthesis is illustrative (Scheme 4.136). Treatment of the cyclo-... 

The Diels-Alder reaction outlined above is a typical example of the utilization of axially chiral allenes, accessible through 1,6-addition or other methods, to generate selectively new stereogenic centers. This transfer of chirality is also possible via in-termolecular Diels-Alder reactions of vinylallenes [57], aldol reactions of allenyl eno-lates [19f] and Ireland-Claisen rearrangements of silyl allenylketene acetals [58]. Furthermore, it has been utilized recently in the diastereoselective oxidation of titanium allenyl enolates (formed by deprotonation of /3-allenecarboxylates of type 65 and transmetalation with titanocene dichloride) with dimethyl dioxirane (DMDO) [25, 59] and in subsequent acid- or gold-catalyzed cycloisomerization reactions of a-hydroxyallenes into 2,5-dihydrofurans (cf. Chapter 15) [25, 59, 60],... 

Ireland-Claisen rearrangement as an alternative approach to the syn isomer with a high degree of diastereoselectivity was also examined. This reaction might be similar to the system of ester-enolate [2,3]-Wittig shift in the case of OR (R=protective group). 

The (panial) description of the synthesis and coupling of the live fragments starts with the cyclohexyl moiety C21—CM The first step involved the enantio- and diastereoselective Sharpless epoxidation of l,4-pentadien-3-ol described on p 126f The epoxide was converted m four steps to a 3-vinyl 6-lactone which gave a 3-cydohexenecarboxylate via Ireland-Claisen rearrangement (cf p 87) Uncatalysed hydroboration and oxidation (cf. p 131) yielded the desired muis-2-methoxycydohexanol which was protected as a silyl ether The methyl car-... 

The C20 amino acid (2.V,3.S, 8.S, 9.S, 4/ , 6 )-3-amino-9-methoxy-2,6,8-tri-methyl-10-phenyldeca-4,6-dienoic acid (Adda 19) is a molecule of interest to biologists and organic chemists as a component of the hepatotoxic cyclic peptides called microcystins. Kim and Toogood used Ireland-Claisen rearrangement in their successful synthesis of Adda8 (Scheme 1.3h). The ester 20 underwent highly diastereoselective Ireland-Claisen rearrangement to provide the acid 21. Conversion of this acid to the phosphonium bromide 22 was achieved in nine... 

In the enantioselective total synthesis of p-lactone enzyme inhibitor (-)-ebelactone A and B, I. Paterson and coworkers constructed seven stereocenters and a trisubstituted alkene plus a very sensitive p-lactone ring. The backbone of their strategy applied an aldol reaction / Ireland-Claisen rearrangement sequence and used minimal functional group manipulation. The Ireland-Claisen rearrangement was performed in the presence of an unprotected ketone moiety and set a precedent for this protocol. The diastereoselectivity was 96 4, indicating highly ( )-selective silylketene acetal formation. 

Corey, E. J., Lee, D. H. Highly enantioselective and diastereoselective Ireland-Claisen rearrangement of achiral allylic esters. J. Am. Chem. Soc. 1991, 113, 40264028. 

Alternatively, the central synthetic building block can also be generated via a diastereoselective Ireland-Claisen rearrangement of butenyl methoxyacetate. Introduction of the styryl fragment results from a Horner-Wadsworth-Emmons reaction. The remainder of the synthesis is closely related to the sequence described above. [51, 52]... 

Panek et al. have made extensive use of this feature of the Ireland-Claisen rearrangement (Scheme 4.21) [24]. Treatment of the (J )-0-methyl glycolate with LDA and TMSCl gave the acid in excellent yield and diastereoselectivity. The resulting allyl silanes were used as nucleophiles in diastereoselective S/ additions. 

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