Formaldehyde hydrazone

Formaldehyde hydrazones react with N,AT -thiocarbonyldi-1,2,-4-triazole to give hydra-zones of thioglyoxalyl-1,2,4-triazoles, which react readily under displacement of 1,2,4-triazole with nucleophilic reagents such as amines and hydrazines but also with less nucleophilic compounds, including hydrazones, sulfonylhydrazides, thiosemicarbazides, and hydrazides.[10]... 

The Michael addition of formaldehyde hydrazone of (S)-1 -amino-2-(methoxymethyl)pyr-rolidine to nitroalkenes gives P-nitrohydrazones in good chemical yield and stereoselectivity (Eq. 4.70).89... 

In 2008, the same group employed chiral dicarboxylic acid (R)-5 (5 mol%, R = 4- Bu-2,6-Me2-CgHj) as the catalyst in the asymmetric addition of aldehyde N,N-dialkylhydrazones 81 to aromatic iV-Boc-imines 11 in the presence of 4 A molecular sieves to provide a-amino hydrazones 176, valuable precursors of a-amino ketones, in good yields with excellent enantioselectivities (35-89%, 84-99% ee) (Scheme 74) [93], Aldehyde hydrazones are known as a class of acyl anion equivalents due to their aza-enamine structure. Their application in the field of asymmetric catalysis has been limited to the use of formaldehyde hydrazones (Scheme 30). Remarkably, the dicarboxylic acid-catalyzed method applied not only to formaldehyde hydrazone 81a (R = H) but also allowed for the use of various aryl-aldehyde hydrazones 81b (R = Ar) under shghtly modified conditions. Prior to this... 

N — n = CH mw 84.08, N 66.64% lt-yel prisms (from eth or benz), mp 125-26°(dec) readily sol in w ale si sol in eth benz can be prepd by reduction of sym-tetrazine with H2S in cold aq soln, or with Zn dust glac acetic acid in ether and from hydrazo-formaldehyde-hydrazone by soln in dil glac acetic acid (Refs 1,2,3 4). Its expl props were not detd... 

Lambert, C.E. Shank, R.C. (1988) Role of formaldehyde hydrazone and catalase in hydrazine-induced methylation of DNA guanine. Carcinogenesis, 9, 65-70... 

A third method for the preparation of 2,3,4,5-tetrahydro-l,2,4-triazines is to react hydrazines with primary amines and formaldehyde (78HC(33)189, p. 630). The first step here is probably the formation of a formaldehyde hydrazone (811 R6 = H) which reacts with another molecule of formaldehyde to give compound (813), the structure of which is similar to (809). 

Thiamine-catalyzed transformations are reversible, thus TV,/V-dialkyl hydrazones were selected as alternative acyl anion equivalents that were reported to react with electrophiles without acidic activation.41 One especially reactive example, formaldehyde hydrazone resin 13, was constructed from polymer-supported hydrazines and was employed in the first polymer-supported, uncatalyzed acyl anion additions (Fig. 8).38 As test substrates, nitroalkenes (as Michael acceptors) and activated aldehydes were selected. Reactivity of these acyl anion equivalents depended critically not only on the nature of the starting hydrazine, but also on the protocol for hydrazine formation. 

For hydrogen bonds weaker than OH 0=C or NH 0=C, theory predicts smaller differences in the X-H bond lengths and negligible changes in the nonhydrogen bonds. TWo models have been studied theoretically with the ab-initio molecular orbital method at the HF/3-21G level of approximation. These are formaldehyde oxime cyclic dimer versus the monomer [378] and formaldehyde hydrazone cyclic dimer versus the monomer [379]. Except for the O-H and N-H bonds, these differences are too small to be detected by single crystal X-ray or neutron diffraction methods, as shown in Fig. 5.2. 

Minh Tho, N., Vanquickenborne, L. G. Mechanism of the Beckmann rearrangement of formaldehyde oxime and formaldehyde hydrazone in the gas phase. J. Chem. Soc., Perkin Trans. 21993,1969-1972. 

Formaldehyde hydrazones behave as nucleophiles in the reaction with aldimines. Chiral adducts are produced by conducting the reaction with octahydro-lB. ... 

As formaldehyde hydrazones are particularly stable towards hydrolysis or polymerization, they can be used in water, a solvent that enhances the reactivity of the azomethine carbon for nucleophilic addition to a-keto esters, to give highly functionalized tertiary alcohols. A significant solvent isotope effect points to the active participation of water as an acid catalyst. ... 

Acetyl chloride has been used as a ketene precursor to prepare P lactams unsubstituted at C3. Unsubstituted imine fragments pose special difficulties in the Staudinger reaction. Formaldehyde imines are difficult to prepare and handle, and generally p-lactams unsubstituted at C4 are not readily accessible. By contrast, formaldehyde hydrazones are more stable and can be used in place of the unstable imines in the Staudinger reaction to afford 4-unsubstituted P-lactams. ... 

The Lewis acid/oxime [66] and the formaldehyde/hydrazone [127, 128] capping processes permit the assembly of clathrochelate iron(II) or cobalt(II) complexes [M(L1001)]+ to [M(L1006)]+ based on miscellaneous oxime-hydrazone ligand systems (Eq, 4,34) [129, 130],... 

TBDMS triflate promotes the conjugate addition of formaldehyde hydrazones to a,)3-unsaturated ketones and lactones (eq 24). Another bulky silylating agent, dimethyl(l,2,2-tri-methylpropyl)silyl (TDS) triflate, has also been used to the same effect with enones. ... 

An innovative development in the use of Enders chiral hydrazines involves reaction of the formaldehyde hydrazone 87 as a chiral formyl anion equivalent (Scheme 12.13) [93, 94]. Hydrazone 87 adds to nitroolefms to afford the corresponding adducts with excellent diastereoselectivity. Addition of 87 to nitroolefm 88, for example, proceeded to furnish 89 in 93 % yield and dr >99 1. The resulting adduct could subsequently be converted into aldehyde 91 (> 98 % ee) by ozonolytic cleavage or into nitrile [95] 92 (> 99 % ee) under mild oxidative conditions by treatment with magnesium monoperoxyphthalate (90) [94]. 

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