Carroll rearrangements

3 Palladium-Catalysed Allylic Alkylation 4.3.1 Carroll Rearrangement 

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The rearrangements of various allylic compounds catalyzed by both Pd(II) and Pd(0) are treated in this section[491]. Related reactions such as the Carroll rearrangement are treated in Section 2.10.1 and the Pd(II)-catalyzed Cope rearrangement is treated in Chapter 5, Section 3. 

Claisen and Carroll rearrangements of hydroxyalkenylsilanes provide an asymmetric synthesis of allylsilanes from optically active secondary alcohols39,40. 

However, if only two carbon atoms are present (15) they may be disconnected to give an allylic alcohol 16 and the acetoacetic ester, through a retro-Carroll rearrangement [6] (Scheme 7.6). 

The method of preparation of 5-dodecen-2-one presented here is a version of the literature procedure published earlier. It offers several advantages over existing methodology (1) The ester enolate modification of the Carroll rearrangement provides the allylic acetoacetates via a mild, fast, and high yield synthesis. This procedure represents a significant Improvement over... 

The Carroll Rearrangement Synthesis of 5-Dodecen-2-one S. R. Wilson and C. E. Augelli, Department of Chemistry,... 

The Carroll rearrangement, a variation on the ester Claisen rearrangement, is a useful method for the preparation of y, 8-unsaturated ketones from allyl acetoacetates, and has been adapted to provide a method for the synthesis of a number of specific arylacetones. Thus, treatment of the p-quinol 1 with diketene and a catalytic amount of DMAP at room temperature gave a 72% yield of the arylacetone 2 together with 5% of the benzofuran 3. 

The reductive coupling of the 7i-allylpalladium enolates 400 gives the allylated ketones 403. This reaction is also possible thermally and is called the Carroll reaction. Whereas the Carroll reaction proceeds by heating up to 200 °C, the Pd-catalysed Carroll-type reaction can be carried out under mild conditions (even at room temperature) by reductive elimination of the 7t-allylpalladium enolate 400 [177,178], The Pd-catalysed reaction is mechanistically different from the thermal reaction and more versatile, which is explained by the [3,3] sigmatropic rearrangement of the enolate form. For example, thermal Carroll rearrangement of the a,a-disubstituted keto ester 410 is not possible, because there is no possibility of the enolization. However, it rearranges to ketone 411 smoothly with the Pd catalyst, via the 7i-allylpalladium enolate. 

Asymmetric decarboxylative rearrangement (Carroll rearrangement) of allyl a-acetamido-/3-ketocarboxylates, catalysed by a palladium complex modified with a chiral phosphine ligand, has been reported to give optically active /,5-unsaturated a-amino ketones with up to 90% ee (Scheme 92).135 The mechanism for the Carroll rearrangement is shown in Scheme 93. 

By the Carroll rearrangement, 2-methyl-2-hepten-6-one (8.34) from commercially available materials such as acetone, acetylene and ethyl acetoacetate is synthesized (Scheme 8.13). 

Among the most favorable features of the Carroll variant of the Claisen rearrangement are the relative ease of preparation of the parent system by condensation of allylic alcohols with acetoacetic estet or di-ketene and the defined configuration of the intermediately generated double bond. The Carroll rearrange-... 

An improved version of the Carroll reaction, the ester enolate Carroll rearrangement, was reported in 1984 by Wilson and Ptice. Dianions of allylic acetoacetates, generated by treatment with 2 equiv. of LDA at -78 °C in THF, were rearranged at room temperature or 65 C to yield >keto acids in 40-80% yield (equation 12). In the course of a synthesis of the sesquiterpene isocomene, Snider and Beal used this method for the rearrangement of acetoacetate (73), prepared in 83% yield from reaction of cyclopen-tene (72) with diketene and a catalytic amount of DMAP (Scheme 11). The ( )-isomer of ketone (74) is obtained stereospecifically, since there is a severe steric interaction between the methyl groups in the Carroll rearrangement transition state leading to the (Z)-isomer. 

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