Migration dimethylamino groups

Scheme 13 Possible mode of formation of the cyclopentadiene 61 isomeric with 60a by 1,2-migration of the dimethylamino group via a bridged zwitterionic intermediate 62 [44]...

The formation of the tricarbonylchromium-complexed fulvene 81 from the 3-dimethylamino-3-(2 -trimethylsilyloxy-2 -propyl)propenylidene complex 80 and 1-pentyne also constitutes a formal [3+2] cycloaddition, although the mechanism is still obscure (Scheme 17) [76]. The rf-complex 81 must arise after an initial alkyne insertion, followed by cyclization, 1,2-shift of the dimethylamino group, and subsequent elimination of the trimethylsilyloxy moiety. Particularly conspicuous here are the alkyne insertion with opposite regioselectivity as compared to that in the Dotz reaction, and the migration of the dimethylamino functionality, which must occur by an intra- or intermo-lecular process. The mode of formation of the cyclopenta[Z ]pyran by-product 82 will be discussed in the next section. 

The first example of an iminophosphenium salt (18) with a P—C bond was obtained by irradiation of the azidophosphonium salt 17 during which migration of a dimethylamino group occurs migration of the phenyl group leads to 19 (equation 9)37. 

This procedure gives a synthetically useful example of the Fritsch-Wiechell-Buttenberg rearrangement [95,204]. The intermediate anionic species cannot be intercepted, because it immediately loses potassium chloride with simultaneous migration of a dimethylamino group. Other ynediamines can be prepared in a similar way. The ynediamine is extremely water-sensitive, so that a dry work-up is required. 

Me, 2-Pr, X = Y = Cat) was found to depend on solvent and temperature <85ZOBi982>. A quite remarkable reaction shown in Equation (6) involves a 1,3 migration of a dimethylamino group (Y) from one phosphorus atom to the other at some stage during the reaction <93PS(75)233>. 

Treatment of the 2-tosylate (208) with sodium azide in DMF gave the 3-azido derivative (209), presumably by ring-opening of an aziridinium ion intermediate." This appears to be the first example of the migration of a dimethylamino-group on a pyranose ring during a displacement reaction. 

The migration of the dimethylamino-group in the methyl pyranoside (52) (see Vol.ll, p.8l) has been Investigated in detail. In polar solvents such as water, the aziridonium salt (53) is formed rapidly, and is then opened by a nucleophile to give derivatives (54), but in non-polar solvents the migration appears to be concerted, and an equilibrium mixture of compounds (52) and (55), in the ratio 1 2, is formed (Scheme 14). ... 

Squaric dithiones (16 X = S) react with an amine to give transamination with intramolecular migration of a sulphur atom. -Methylated cations are obtained with methyl fluorosulphonate, and on hydrolysis lose a dimethylamino-group to give a ketone. Reactions of a cyclobutenedithione with a thiocyanate and reaction of a monothiosquarate dianion have been reported. 

A. Hasegawa, M. Goto, and M. Kiso, An unusual behavior Of methyl or benzyl 3-azido-5-0-benzoyl-3,6-dideoxy-a-L-talofuranoside with (dimethylamino) sulfur trifiuoride migration of the alkoxyl group from the C-l to the C-2 position, J. Carbohydr. Chem. 4 627 (1983). 

The levulinoyl esters are prepared from the free hydroxyl group by treatment of levulinic acid with DCC [255,256] or l-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDAC) [257] in the presence of DMAP (O Scheme 38). Additionally, 3 - and 5 -0-levulinyl protected derivatives of 2 -deoxy nucleosides have been prepared by regioselective enzymatic acylation using a variety of lipases and acetonoxime levulinate as acylating agent [258]. In contrast to other ester substituents, the 0-levulinoyl group is far less prone to migration [259]. 

Modifications of both saccharide moieties of erythromycin have also been made. Migration of the 3 -dimethylamino substituent to C-2 has been demonstrated [138]. Acylation of the 4"-hydroxyl group yielded products such as A-63075 (4"-0-carbamoylclarithromycin), which minimize gastrointestinal side effects in dogs [139]. Modifications of the 4"-hydroxyl group also increase activity against certain erythromycin-resistant bacteria [140, 141],... 

This reaction has been extended to the translocation of the acyl group for indole derivatives. In addition, a chiral planar DMAP derivative has been developed and applied for the enantioselective rearrangement of 0-acylated azlactone and the same catalyst recently has been used for an intermolecular reaction to form 1,3-diketones. Moreover, 3-(2,2,2-triphenyl-1 -acetoxyethyl)-4-(dimethylamino) pyridine (TADMAP) has been applied as a chiral nucleophilic catalyst to catalyze the carboxyl migration of oxazolyl, furanyl, and benzofuranyl enol carbonates with good to excellent levels of enantioselec-tivity. The rearrangement for oxazole derivatives are particularly efficient for giving chiral lactams and lactones. ... 

The procedure for the chlorosulfonation of azobenzene was first reported by PearP and was successfully repeated by Cremlyn. The comparatively drastic conditions required for the reaction 414— 415 (Equation 128) are probably due to initial protonation of the azido group in the strongly acidic medium. Attempts were made to extend the procedure to the chlorosulfonation of other azobenzenes. With 4-acetamidoazobenzene, extensive decomposition occurred at 125 °C, which may arise from acid-catalysed migration of the acetyl group into the aromatic nucleus, followed by decomposition of the resultant free amine intermediate. However, when the reaction temperature was reduced to 80 C, a low yield of the 4 -sulfonyl chloride was isolated. On the other hand, similar efforts to chlorosul-fonate p-(A iV-dimethylamino)azobenzene failed to yield a pure product,but more recently debsyl chloride 416 has been synthesized and is used as a derivatization reagent in HPLC for the separation of amines and amino acids. ... 

Methyl migrates less readily than benzyl or even homologous alkyl groups do. This rule applies also to A -ylides and a-lithiated amines 346. Outpacing methyl completely, benzyl, cinnamyl, and 2-(dimethylamino)ethyl migrate exclusively to afford the rearranged lithium amides at +25 °C in 70-90% yield (Scheme 1-271). ... 

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