Claisen-Johnson Orthoester Rearrangement

Johnson-Claisen Rearrangement (Johnson Orthoester Rearrangement)... 

Johnson et al. used their newly developed orthoester Claisen reaction to achieve a highly stereoselective total synthesis of aM-trans squalene (5)1 (Scheme 1.20. The diene diol 6 underwent Johnson-Claisen rearrangement when it was heated with ethyl orthoacetate in the presence of propionic acid for 3 h at 138 C. The diene dialdehyde 7, obtained by treatment of the resulting ester with lithium aluminum hydride followed by oxidation with Collins reagent, reacted with 2-propenyllithium to give the tetraene diol 8. The tetraene dialdehyde 9, which... 

For the application of the Johnson orthoester Claisen rearrangement to a similar system see A. Srikrishna and R. Viswajanani, Tetrahedron Lett., 1996, 37, 2863. 

Jones, G.B., Huber, R.S., and Chau, S. 1993. The Claisen rearrangement in synthesis Acceleration of the Johnson orthoester protocol en route to bicychc lactones. Tetrahedron, 49 369-80. 

Extremely useful ramifications of the Claisen rearrangement emerged with Johnson s discovery of the orthoester variant of this transformation. His approach (Scheme 2.156) involved the following sequence of steps, which were carried out in one reaction vessel (i) transesterification of the orthoester with an allylic alcohol to give 490 (ii) elimination to form the intermediate ketene acetal 491 and (iii) [3,3] sigmatropic rearrangement to yield the y, -unsaturated ester 492. The Johnson-Claisen procedure is properly considered to be one of the most efficient methods available to prepare y,(5-unsaturated esters such as 492. ° ... 

Whereas Eschenmoser and Johnson variants of the Claisen rearrangement utilize an excess of amide acetal and orthoester precursors, respectively, for generation of the vinyl ether functionality, the Carroll... 

Jones, G. B., Huber, R. S., Chau, S. The Claisen rearrangement in synthesis acceleration of the Johnson Orthoester Protocol en route to bicyclic lactones. Tetrahedron 1992, 49, 369-380. 

In their short synthesis of ( - )-162, Pearson and Hembre also began with the protected D-erythronolactone derivative 197, which was converted in three steps into a mixture (97 3) of diastereomeric allylic alcohols 203 (Scheme 29) 127). Separation of the epimers, although possible, was not necessary as both alcohols yielded the same product 204 after Johnson orthoester Claisen rearrangement. Subsequent Sharpless asymmetric dihydroxylation with AD-Mix-p gave as major... 

Most [3,3]-sigmatropic rearrangements take place thermally, and the Cope, oxy-Cope and Claisen rearrangements are among the most important rearrangements in this class. Important variants of the Claisen rearrangement include the Johnson modification via orthoesters, the Eschenmoser modification via ketene N,O-acetals, the Ireland modification via ketene silylacetals and the Corey modification via boron ester enolates [696], The aza-Claisen rearrangement has also seen... 

Tetraethynylmethane (39), a potential monomer for a three-dimensional superdiamonoid carbon network [1], was elusive for many years [51, 52], until its synthesis was accomplished in 1993 by Feldman and co-workers [53]. The key step in the synthesis was the acid-mediated Johnson orthoester variant of the Claisen rearrangement, which provided the central quaternary methane C-atom with suitable functional groups for the ultimate transformation into 39 [Scheme 13-9(b)]. Solid 39, like tetraethynylethene (20), decomposes rapidly at room temperature in either the presence or absence of oxygen. The earlier efforts to prepare tetraethynylmethane had yielded the peralkynylated derivatives 40-42 [Scheme 13-9(c, d)] [51, 52]. Tetraethy-nylallene represents another potential precursor for a three-dimensional carbon network [1], but remains elusive of the perethynylated [K]cumulenes, so far only the silyl-protected [3]cumulenes 43a and 43b [Scheme 13-9 (e)] have been prepared [54]. With 44 [Scheme 13-9 (f)], the first transition metal complex of a perethynylated ligand is now available [55]. 

This reaction was first reported by Johnson et al. in 1970. It is a highly stereoselective synthesis of y,5-unsaturated esters from the reaction between allylic alcohols and an orthoester in the presence of a trace amount of weak acid, such as propionic acid. Because this reaction is the modification or variant of the Claisen Rearrangement, it is often referred to as the Johnson orthoester Claisen rearrangement. Occasionally, this reaction is also known as the Claisen-Johnson orthoester rearrangement, " or Johnson orthoester protocol. This reaction involves the formation of mixed orthoester from allyl alcohol and the added orthoester, which loses an alcoholic component to form a ketene acetal then migrates to unsaturated carbonyl compounds via the Claisen Rearmagement with high syn selectivity. Posner further extended this reaction to use sulfonyl orthoester. Overall, this reaction has been applied to the synthesis of a variety of complicated natural products, such as squalenes. ... 

Other references related to the Johnson orthoester Claisen rearrangement are cited in the literature. ... 

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