Rearrangements conditions

Attack on the electrophilic C-2 may occur as in the 2-aminothiazoles series, which probably explains the rearrangements observed in acidic medium (121, 711, 712, 723, 724), in aqueous medium with NaOAc (725), or with aqueous NaHCOj (725) (Scheme 232). That the initial attack probably involves the C-2 atom is substantiated by the fact that this rearrangement occurs under extremely mild conditions for 2-iinino-3-substituted-5-nitro-4-thiazolines (725). As the whole mechanism proposed (see p. 92) is reversible, when imino derivatives are submitted to such rearrangement conditions the rearrangement is expected to occur faster if steric interaction between 3- and 4-substituents exists in the 2-imino isomer. Another reaction may occur in acidic medium phenylimino-2-bipheny]-3,4-4-thiazoline hydrolyzed with hydrochloric acid gives the corresponding 4-thiazoline-2-one and aniline (717). 

When an a-hydroxy amide is treated with Br2 in aqueous NaOH under Hofmann rearrangement conditions, loss of C02 occurs and a chain-shortened aldehyde is formed. Propose a mechanism. 

Optimized rearrangement conditions in presence of excess silylketene acetal. Rearrangement in the presence of dihydropyrane, re-addition of PhSeOH. 

The E- and Z-adducts were separately subjected to the thermal rearrangement conditions, as shown in Scheme 6.5. The thermal rearrangement of the Z-adduct 8Z occurred at a lower temperature (125 °C) and gave a 72% assay yield of product 3. On the other hand, thermal rearrangement of the T-adduct 8E required higher temperature (135 °C) and gave a lower assay yield. Both of the reactions generated about 5% of imidazole 27 as a by-product. In order to improve the assay yield and... 

Other evidence, for instance the observation of a semidine as one of the reaction products,256 led to the realization that the reaction is a benzidine disproportionation, such as those observed when benzidines with two p-substituents are subjected to benzidine rearrangement conditions 260,261 this also very conveniently explains the products formed. The mechanism is given in Scheme 13.258... 

The methods for synthesis of starting cyclic dienes, the rearrangement conditions and kinetic characteristics of basic substrate reactions over a wide range of substitution variations were generalized in work97 which included a quite detailed survey of related publications. 

Under Pummerer rearrangement conditions, a-methylthio amide 248 affords a mixture of 2-piperidone 249 and pyridin-2-(3//)-one 250 (86CPB1061). 

Novel a,/ -unsaturated amide derivatives at C(4) of chromones 335 were synthe-sized (equation 124). Oximes 332 and 333 rearranged in the presence of PCI5 into the same amides 335 in high yields. Spiroisoxazolines 334, formed from oxime 332 by acid treatment, also produce 335 under Beckmann rearrangement conditions. 

Under the same standard rearrangement conditions, the analogous a-chloroxime 340 gave a low yield of an azacardenolide 341 (14%) as a result of the normal Beckmann rearrangement the nitrile 342 was isolated as the major reaction product (equation 128). 

Oxidation of the pyridoins, e.g. with iodine, gives the corresponding a-diketones. The significant electron withdrawal exerted by the 7r-deficient heterocyclic system on carbonyl groups at the a- and y-positions can be demonstrated in the behaviour of the diketones under benzilic acid rearrangement conditions. Whereas 3,3 -pyridil (73) gives a normal... 

The rearrangement cannot involve the addition and elimination of the alcohol because the rearrangement takes place with powdered potassium hydroxide in the absence of alcohol. In addition, 2-ethoxy- 1-pentene was shown to remain largely unchanged under the rearrangement conditions, and it affords no alkynes or allenes. A probable mechanism involves the removal of a proton by the base to give the anion. 

In the reaction of the hydroxy ester (87) with methylmagnesium iodide the process stops at the ketone (91) stage. The pinacols were investigated under various pinacolone rearrangement conditions.144 By a Grignard reaction of 2-cyanoquinuclidine (92), 2-benzoyl-quinuclidine (93) has been prepared.49... 

Methyl-2-twistanol rearranges to the 2-methyl-2-adamantyl cation in SbFs /S02 solutions 40 The mechanism of this rearrangement can be most readily depicted in terms of 1,3-hydride shifts (protonated cyclopropanes) as illustrated in Scheme 7. Control experiments have shown that the 3-methyl-l-adamantyl cation is not involved in the rearrangement. It is stable to the rearrangement conditions despite the fact that relative solvolytic reactivities suggest that the 2-methyl-2-adamantyl cation is more stable by nearly 6 kcal/ mole 55> 56 ... 

Methods for the construction of the thieno[2,3-c]pyridine skeleton based on the formally simultaneous formation of both the pyridine and thiophene rings were documented. Under the Pummerer rearrangement conditions, ( -s ul liny lain idc 222 underwent a cascade transformation into 223, which was oxidized to fused lactam 224 in low yield (1999JOC2038). Data on the use of cascade transformations, including the Pummerer rearrangement - cycloaddition sequence, in the synthesis of complex heterocyclic systems were summarized in a review (1997S1353). 

Under Payne rearrangement conditions, sodium /-butylthiolate provides 1 -/-butylthio-2,3-diols with very high regioselectivity. The selectivity is affected, however, by many factors including reaction temperature, base concentration, and the rate of addition of the thiol. These sulfides can then be converted to the l,2-epoxy-3-alcohols, which in turn react with a wide variety of nucleophiles specifically at the 1-position (Scheme 9.6). This methodology circumvents the problems associated with the instability of many nucleophiles under Payne conditions.85... 

Conventional chemistry converted carbinol 277 into acyl azide 278, which was treated under Curtius rearrangement conditions to obtain either amine 279 or urea derivative 280, the respective precursors of guanine derivative 281 and thymidine analogue 282. 

Under Beckmann rearrangement conditions, O-tosyl oximes furnish the cyanoanilines, while the parent oxime gives the intermediate 2-cyanophenylisocyanate220. When the O-acetyl oximes are reacted with sodium azide, cyanoanilines are also produced. Campbell proposed a mechanism where the E-isomer of the oxime suffers elimination, forming a 2-cyanoisocyanate, which upon hydrolysis and decarboxylation gives 2-cyanoani line (Scheme... 

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