Metals Claisen rearrangement

The cw-isobacteriochlorin 16A formed by the Claisen rearrangement has been utilized for the further transformation into porphyrin dp2311 0 the metal-free ligand of heme dr... 

Dehydrobromination of bromotrifluoropropene affords the more expensive trifluoropropyne [237], which was metallated in situ and trapped with an aldehyde in the TIT group s [238]synthesis of 2,6-dideoxy-6,6,6-trifluorosugars (Eq. 77). Allylic alcohols derived from adducts of this type have been transformed into trifluoromethyl lactones via [3,3] -Claisen rearrangements and subsequent iodolactonisation [239]. Relatively weak bases such as hydroxide anion can be used to perform the dehydrobromination and when the alkyne is generated in the presence of nucleophilic species, addition usually follows. Trifluoromethyl enol ethers were prepared (stereoselectively) in this way (Eq. 78) the key intermediate is presumably a transient vinyl carbanion which protonates before defluorination can occur [240]. Palladium(II)-catalysed alkenylation or aryla-tion then proceeds [241]. 

N Claisen rearrangement.3 This Pd(II) salt permits the rearrangement of S- llylthioimidates to N-allylthioamides. Tetrakis(triphcnylphosphine)palladium and various other metal salts are inactive. The rearrangement is inhibited by a substituent til the 2-position of the allyl group. 

BINAP, 127, 171, 191, 194, 196 olefin reaction, 126, 167, 169, 191 organic halides, 191 Pancreatic lipase inhibitors, 357 Pantoyl lactone, 56, 59 para-hydrogen, 53 Peptides, matrix structure, 350 Perhydrotriphenylene, crystal lattice, 347 Pericyclic reactions, 212 chiral metal complexes, 212 Claisen rearrangement, 222 Diels-Alder, 212, 291 ene reaction, 222, 291 olefin dihydroxylation, 150 Phase-transfer reactions asymmetric catalysis, 333... 

Mercury(II) oxide and acetic acid effect the cyclization of l,4-diaryloxybut-2-ynes to 4-aryloxymethylchromenes. The transformation was attributed to cyclization of the butanone which resulted from hydration of the alkyne (72JHC489). However, it has since been shown that similar butanones do not cyclize to chromenes under the cyclization conditions (78JOC3856). Instead, a mechanism is proposed which involves a charge-induced Claisen rearrangement which is triggered by 7r-complex formation between the metal ion... 

Anionic oxy-Claisen rearrangement.2 The [3,3] Claisen rearrangement of en-olates of a-allyloxy ketones is markedly dependent on the nature of the metal hydride used, and to a less extent, the solvent. An example is the rearrangement of a-(allyloxy)propiophenone (1) to the a-hydroxy ketone 2. The rearrangement... 

Claisen rearrangements in heteroaromatic systems, 42, 203 in nitrogen heterocyclic systems, 8, 143 Complex metal hydrides, reduction of nitrogen heterocycles with, 6, 45 39, 1 Concept of aromaticity in heterocyclic chemistry, 56, 303 Condensed heterocyclo[n,m- , b, or cjquinazolines, 52, 1 Condensed 4-thiazolidinones, 49, 1... 

The Claisen rearrangement, Cope rearrangement, and associated variants are powerful tools that can be used to create a number of new chiral centers in an expeditious manner, but the use of heavy metals, such as mercury, should be avoided. Of these reactions, the Ireland-Claisen ester enolate reaction provides the most versatile synthetic pathway with minimal scale up problems. 

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