Rearrangement of allylic acetals

Allylic ester rearrangement is catalyzed by both Pd(II) and Pd(0) compounds, but their catalyses are different mechanistically. Allylic rearrangement of allylic acetates takes place by the use of Pd(OAc>2-Ph3P [Pd(0)-phosphine] as a catalyst[492,493]. An equilibrium mixture of 796 and 797 in a ratio of 1.9 1.0 was obtained[494]. The Pd(0)-Ph3P-catalyzed rearrangement is explained by rr-allylpalladium complex formation[495]. 

Rearrangement of allylic acetals. 3-Acetylpyrrolidines can be obtained in good yield by an acid-catalyzed rearrangement of 5-methyl-5-vinyloxazolidines. The rearrangement involves an aza-Cope rearrangement followed by Mannich cycli-zation (equation I).1... 

This rearrangement of allylic acetals can also be used for furan annelations, in which the formation of the new tetrahydrofuran ring is coupled with ring enlargement of the starting ring.3 The same dr-fused bicyclic tetrahydrofuran is formed from either one of the cis- or mwr-allylic diols used as starting materials. 

An example of catalytic oxypalladation is the rearrangement of allylic acetates with Pd ll). The reaction starts with oxypalladation of the alkene and it is the acetate already present in the molecule that provides the nucleophile to attack... 

Lewis acids such as silyl triflates7 or boron trifluoride8 initiate the rearrangement of allyl acetates, usually with low stereoselectivity. But soft electrophilic metal ions such as Hg2+ or Pd2 + catalyze the rearrangement of allylic esters and carbamates (Table l)9. 

Table 2. Stereoselective Palladium(II)-Catalyzed Rearrangements of Allylic Acetates... 

Lewis acid-promoted (SnCU or Et2AlCl) rearrangements of allylic acetals provide substituted tetrahydrofurans [80]. Upon addition of SnCU, 4,5-dimethyl-2-phenyl-4-vinyl-l,3-dioxolane rearranges to the all-cw furan (Eq. 48). No racemization is observed with opti-... 

The best known example of this kind is the rearrangement of allyl acetates, a synthetically very useful reaction, especially in the case of tertiary systems (equation 10). These undergo isomerization sometimes even under the conditions of acetylation. OAerwise, Lewis acid catalysis, preferably with PdCl2(MeCN)2, will bring about the isomerization smoothly (equation 11). ... 

Hopkins, M. H., Overman, L. E. Stereocontrolled preparation of tetrahydrofurans by acid-catalyzed rearrangement of allylic acetals. J. Am. Chem. Soc. 1987, 109, 4748-4749. 

Derivative 441 is an extremely useful intermediate for the construction of highly functionalized chiral tetrahydrofiirans via Lewis acid-promoted rearrangement of allylic acetals. This is elegantly demonstrated by the synthesis of optically pure (-h )-muscarine tosylate (446) [138] (Scheme 62). 

The stannic chloride-catalyzed rearrangement of allyl acetals to tetrahydrofurans (Equation (95)) has been studied extensively <91JA5354,9UA5365,91JA5378>. 

Representative procedure for the gold-catalyzed rearrangement of allyl acetates. 4-Nitrocinnamyl... 

An early example that shows the importance of the tuning of the steric properties of the ligands used was reported by Nolan and coworkers. They found that in the gold-catalyzed rearrangement of allyl acetates (see Scheme 9.20), only the use of the very sterically encumbering ICy and IPr ligands provided the... 

Scheme 9.20 Gold-catalyzed rearrangement of allyl acetates according to Nolan and coworkers [39].

A further application of cyclization-induced [3,3] sigmatropic rearrangements cf. 3, 146) has appeared in the rearrangement of allylic acetates catalysed by soluble Pd" salts (Scheme 25) at room temperature to give an overall... 

The [3,3]-sigmatropic rearrangement of allylic acetates, catalysed by soluble Pd salts, that was reported last year (4,152) as a method for [1,3]-oxygen transposition has recently been shown to occur suprafacially with complete chirality transfer an example is the conversion (70) (71). Overman has... 

In a stereocontrolled synthesis of prostaglandins possessing either the C-15(5) or the C-15(/ ) configuration, a neat application of a Pd -catalysed [3,3] sig-matropic rearrangement of allylic acetates with conjugate chirality transfer was discovered/ Thus, when either of the two acetates (2) or (3) was treated at 25 °C with bis-(acetonitile)palladium(li) chloride (0.04 equiv.), a single rearranged acetate was produced (Scheme 6). 

Scheme 2.18 Au-catalysed rearrangement of allylic acetates. Relative free energies given in kcalmoCf...

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