Rear-rangement

A neat twofold transformation, obviously a consequence of a sigmatropic [2.3]rear-rangement rather than by an ionic pathway, occurs in the case of a propargyl sulfinate (equation 3). 

MEYKR-SCHUSTER REARRANGEMENT. Acid catalyzed rear rangement of secondary and tertiary a-acetylenic alcohols to a.ft-unsaiurated carbonyl compounds aldehydes when the acetylenic group is terminal, ketones when it is internal. 

Overman, L. E. Kakimoto, M. Okazaki, M. E. Meier, G. P. C-C Bond formation under mild conditions via tandem cationic aza-Cope rear-rangement-Mannich reactions. A convenient synthesis of poly substituted pyrrolidines. 

V.S. Bogdanov et al., The novel thermal rear-rangement in the pyrido[l,2-a]pyrimidine series the transformation of 3-acetyl-4-phenylaminopy-rido[l,2-a]pyrimi-dine-4-on, Mendeleev Commun., 106-107 (1995). 

Fig. 14.20. Second semipinacol rearrangement of a glycol monotosylate. The reaction involves two steps in basic media, since the [l,2]-rear-rangement and the dissociation of the tosylate occur at the same time. Under reaction conditions this rearrangement is followed by a base-catalyzed epimerization. This is why instead of the initially cis-annulated bicyclic ketone D its trans-isomer C is isolated.

Fig. 14.23. Ring expansion of a cyclohexanone via addition of diazoacetic acid ethyl ester and subsequent [l,2]-rear-rangement.

Panzar aMA, Gussoni E, Begovich AB, Murray RS, Zang YQ, Appel SH, Steinman L, Zliang J (1999) T-cell receptor BV gene rear -rangements in die spinal cords and cerebrospinal fluids of padents widi amyoti ophic lateral sclerosis. Neiu obiol Dis 6 392-405. 

It was previously noted that enolates of a-allyloxy ketones were capable of either 2,3- or 3,3-rear-rangement, depending upon counterion, reaction conditions and substituents. Ester enolates show a greater propensity for the 2,3-pathway, as illustrated by the geraniol-derived alkoxyacetate (198) which afforded hydroxy ester (200) as the sole product upon treatment with LDA in THF at -78 to 0 C. The 3,3-product (201) could be obtained by addition of TBDMS-Cl and HMPA to the enolate at -78 °C and thermal rearrangement of the TBS enol ether (199b Scheme 14). ... 

Alkylboranes rearrange intramolecularly (on heating) to thermodynamically more stable alkylboranes, typically with the boron atom attached to the StericaUy least hindered position on the alkyl chain (the hydroboration rear-rangement). " 53 529.533 wjnjams proposed that this equilibrium occurs by a stepwise intramolecular attack of the electron-deficient center on the neighboring C-H o bonds. The transition state of the intramolecular migration incorporates a pentacoordinate carbon atom [Eq. (6.142)] ... 

The observed photobehavior of the benzaldehyde-CDx complexes in the solid state is unique and completely different from that of these complexes in aqueous solution and also from that of benzaldehyde 36 in organic solvents. The substantial formation of 4-benzoylbenzaldehyde 38 upon irradiation in (3- and y-CDx cavities indicates that these medium-sized CDx s provide the radical pair within a fairly spacious supercage environment, thus allowing the para-rear-rangement (Scheme 13). The formation of practically racemic 37 upon irradiation of the y-CDx complex may also be attributed to the looser orientation of benzaldehyde 36 in the y-CDx cavity than in the (3-CDx cavity. It was thus demonstrated that the chiral hydrophobic cavity of native cyclodextrins not only modifies the photoreactivity of the included guest but also functions as a chiral supramolecular environment for photochirogenesis, albeit resulting in only modest ee%. 

Substrate Unrearranged Product(s) Rearranged Alcohol(s) Expected Observed Ratio of Unrearranged to Rerranged Alcohol Rate Constant For Radical Rear-rangement, s-i at45 C... 

Acid Catalyst for Rearrangements. When guaiacol and triethyl orthoacrylate were reacted in refluxing benzene using propionic acid as a catalyst, only 50% of the desired Claisen rear-rangement/ring closure product was obtained, due to esterification of the catalyst. Use of the more hindered pivalic acid furnished the desired product in quantitative yield (eq 1) see also Sato et al. and Dorsey et ah ... 

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