Imine hydrate

Iminium ions formed from an electrophile and an enamine are stable in the absence of a base. Upon aqueous workup they react via the unstable intermediate of an imine hydrate to furnish the corresponding a-functionalized aldehyde or ketone. Iminium ions formed in the presence of a base are deprotonated by this base to give an enamine. The latter is hardly ever isolated, but hydrolyzed upon a somewhat more aggressive workup with diluted... 

Reaction of AT-methy lene-ftrr-bu tvl.i in i n c with octafluoroisobutylene in diethyl ether in the presence of water leads to unexpected l,3,7-oxadiazocan-4-one ring system 155 as a result of the complex sequence of reactions (Scheme 39 <1996ZOB344>). It is believed to include steps of imine hydration, cyclization accompanied by elimination of tert-butylamine, and final hydrolysis of difluoromethyl moiety into carbonyl group. 

Reaction with primary amines (Section 17 10) Isolated product is an imine (Schiff s base) A carbinolamine inter mediate is formed which undergoes de hydration to an imine... 

Ethylene imine Hydrazine hydrate Hydrogen sulfide. Hydroxylamme salts Inorganic Hg. compounds lodates Iodides... 

There are some special cases where tetrahedral intermediates are unusually stable there are three phenomena which lead to this stability enhancement. The first is an unusually reactive carbonyl (or imine) compound which is very prone to addition. An example of such a compound is trichoroacetaldehyde or chloral, for which the covalent hydrate can be isolated. A simple way to recognize such compounds is to think of the carbonyl group as a (very) stabilized carbocation, bearing an substituent. 

Ammonia itself yields imines, R2C=NH, with carbonyl compounds but these derivatives are unstable and react with each other to form polymers of varying size. The classical aldehyde ammonias are found to be hydrated cyclic trimers, but from aldehydes carrying powerfully electron-withdrawing substituents it is possible to isolate the simple ammonia adduct [73, cf. (72), and hydrates, p. 208, hemi-acetals,... 

Similarly, Vasudevan and Verzal have found that terminal alkynes can be hydrated under neutral, metal-free conditions using water as solvent (Scheme 4.15) [41], While this reaction typically requires a catalyst such as gold(III) bromide, employing microwave-superheated distilled water allowed this chemistry to proceed without any catalyst. Extension of this methodology led to a one-pot conversion of alkynes to imines (hydroamination). 

The detailed mechanism of inhibition of TEM-2 (class A) enzyme with clavulanate has been established (Scheme 1) [23,24], The inhibition is a consequence of the instability of the acyl enzyme formed between the /1-lactam of clavulanate and the active site Ser-70 of the enzyme. In competition with deacylation, the clavulanate acyl-enzyme complex A undergoes an intramolecular fragmentation. This fragmentation initially provides the new acyl enzyme species B, which is at once capable of further reaction, including tautomeriza-tion to an entity C that is much less chemically reactive to deacylation. This species C then undergoes decarboxylation to give another key intermediate enamine D, which is in equilibrium with imine E. The imine E either forms stable cross-linked vinyl ether F, by interacting with Ser-130 or is converted to the hydrated aldehyde G to complete the inactivation. 

It has been established that in the Dimroth rearrangement of 2-imino-pyrimidines, water plays an essential role (65JCS7071). In water the imine is, in fact, in equilibrium with its hydrate, the carbinolamine 39. That participation of the hydrate is important is shown by the experimental fact that in dry tetrahydrofuran, acetone, dioxane, or ether, the imine is quite stable and is not inclined to undergo rearrangement. However, on addition of a little water, rearrangement occurs its rate is proportional to the concentration of the water (65JCS7071). 

Solid anilines (236) and solid aromatic aldehydes (77) give the benzylidene anilines 54 upon grinding with 100% yield after drying at 80 °C 20 combinations were performed [101-102] (Scheme 51). A semibatch large-scale experiment of236h with 77b yields quantitatively the hydrated imine 54h that can be dried as well [7]. The reaction of aniline (236s) with benzaldehyde (77k) cannot be run as a solid-state reaction. However, it should be mentioned that the stoichiometric liquid-liquid reaction proceeds with 100% yield because it profits from direct crystallization of the product 54s upon reaction. This technique can... 

Fluoral hydrate and hemiacetals are industrial products. They are stable liquids that are easy to handle, and they react as fluoral itself in many reactions. Thus, in the presence of Lewis acids, they react in Friedel-Crafts reactions. They also react very well with organometallics (indium and zinc derivatives) and with silyl enol ethers.Proline-catalyzed direct asymmetric aldol reaction of fluoral ethyl hemiac-etal with ketones produced jS-hydroxy-jS-trifluoromethylated ketones with good to excellent diastereo- (up to 96% de) and enantioselectivities. With imine reagents, the reaction proceeds without Lewis acid activation. The use of chiral imines affords the corresponding 8-hydroxy ketones with a 60-80% de (Figure 2.49). ° ... 

Imines and (Af,(9)-acetals from fluoral are useful precursors of trifluoromethyl nitrogen-containing molecules amines, amino alcohols, amino acids, peptidomimetic units, heterocycles, and so on (Figure 2.50). These simple Af-derivatives of fluoral are easily prepared from the hydrate or the hemiacetal. Imines of fluoral react in [2 + 1 ]... 

Sowell and co-workers proposed that this may have begun with acid hydrolysis of the imine group to produce hydrazine 188 (Scheme 19), followed by condensation to give the hydrated thienothiadiazole 189. Pummerer-type dehydration then leads to thiadiazole 190. The validity of this proposal, however, has not been investigated. 

Synthesis from Citronellal. One of the oldest routes to hydroxydihydrocitronellal is the hydration of the citronellal bisulfite adduct (obtained at low temperature) with sulfuric acid, followed by decomposition with sodium carbonate. A more recent development is hydration of citronellal enamines or imines, followed by hydrolysis [67]. 

The final, critical oxidative spirocyclization of the 2,3-disubstituted indole to the spiro oxindole was effected by treatment of 124 with tert-butyl hypochlorite in pyridine to provide the labile 125 [Fig. (34)]. The Pinacol-type rearrangement was conducted by treating compound 125 with p-toluenesulfonic acid in THF/water. It is assumed that the chlorination of 124 proceeds from the least hindered face of the indole, to give the a-chloroindolene 125. The hydration of the imine functionality must also occur from the same a-face that is syn to the relatively large chlorine atom furnishing the syn-chlorohydrin 126, that subsequently rearranges stereospecifically to the desired spiro oxindole 127. 

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