HYDRAZONES, fragmentation

The introduction of a phosphorus-containing group into the side chain of the hydrazone fragment of isatin was reported in [97]. The results of a study of the kinetic relationships and mechanism of the addition of dialkyl phosphites to substituted benzylideneamines, which were related to the basicity of the initial amines, were published as abstracts in [98]. 

The nmR chemical shifts of the methyl groups in boron-capped iron(II) diacetylmonooxime hydrazonates (14.0 and 17.7 ppm) are lower than that in the [Fe(thz)](BF4)2 complex (18.6 ppm). A second signal was assigned to the methyl substituent in a hydrazonate fragment. A signal from the azomethine carbon atoms at 168 ppm is also attributed to this fragment, whereas a line at 154 ppm corresponds to an oxime fragment. The NMR... 

The IR spectra of all these complexes also consist of two characteristic very intense and narrow bands of the C-F bond stretching vibrations at 1150-1185 cm-f Apart from the vc=n of oxime groups at 1560-1590 cm-i, characteristic of clathrochelate a-dioxima-tes, for germanium-capped oximehydrazonate clathrochelates, the vc=N of hydrazonate fragments have been observed at 1620 cm-i [73]. 

A useful variant of this chemistry involves the radical cyclization onto an A-aziridinyl hydrazone. Fragmentation of the intermediate nitrogen-centred radical to release nitrogen gas and an alkene (typically styrene or stilbene) results in the formation of a new carbon radical at the original hydrazone carbon atom. Thus, in a synthesis of the sesquiterpene a-cedrene, the radical species 80, formed from the thiocarbonyl compound 79, cychzes onto the hydrazone to give the nitrogen-centred... 

Note that, while the free hydrazine has a planar structure with E-configuration with respect to the N-N bond, the coordinated ligand adopts the Z-conliguration with the phenyl ring rotated by 90° with respect to the hydrazone fragment ... 

Alkylidenehydrazinothiazoles (297) can be prepared either from 2-hydrazinothiazoles (549) or by direct heterocyclization (527). Their characteristic infrared bands have been reported (550). The main mass spectrometric peaks of (4-coumarinyl-2-thiazolyl)hydrazone (302) (Scheme 179) (134, 551) are situated at mle = 361. 244, 243, 118, 216, 202, 174, 117 the proposed interpretation of the fragmentation pattern should, however, be reconsidered. Scheme l80 summarizes some representative reactions of this class of compounds. 

A study of the photochemical reactions of some ylides of compound 1 showed the expected fragmentation to give, from compound 258 for example, 3-methyl-triazolopyridine and the products 259 and 260 postulated as derived from a carhene intermediate (00MI2). Ester 261 gives a hydrazone, and ylide 262 an indolizine. Thermal reactions of ylides are in Section IV. I. 

B. 5-Hexynal. To a solution of 5.60 g. (0.050 mole) of 2,3-epoxycyclohexanone in 120 ml. of benzene in a 500-ml. round-bottomed flask is added 10.82 g. (0.051 mole) of trans-1 -amino-2,3 diphenylaziri-dine.2 Initially, after brief swirling at room temperature, the reaction mixture is a colorless, homogeneous solution however it rapidly turns yellow and cloudy due to separation of water. After 2 hours the benzene and water are removed as an azeotrope under reduced pressure on a rotary evaporator with the bath maintained at approximately 30°. The resulting crude mixture of diastereomeric hydrazones weighs 15.4 g. (Note 7) and is subjected directly to the fragmentation reaction (Note 8). 

Cleavage of carbonyl-containing selenoxides and sulfones Fragmentation of epoxy hydrazones Rearrangement of vinylic hydroxycyclopropanes Rearrangement of 3-hydroxy-1,5-dienes (oxy-Cope)... 

An analogous series of reactions is used to produce depyrimidinated DNA fragments. Hydrazine is used in these reactions, since both cytosine and thymine react with hydrazine. The bases are cleaved to yield urea and a pyrazole ring. The deoxyribose moiety is left as a hydrazone. Piperidine, which reacts with the hydrazone, is used to cleave the nucleotide chain. Cytosines react specifically with hydrazine in 5 mol/ L NaCl, but no specific reaction exists for thymines. Consequently, one aliquot yields labeled oligonu-cleotides 3 -terminated at cytosines, whereas a second aliquot contains nucleotides cleaved in the absence of NaCI at both cytosine and thymine residues. 

Pyrazolo[3,2-c]pyrido[4,3- ][l,2,4]triazine oxides704 were prepared by cyclization of the hydrazone derivatives 703 with ethanolic sodium hydroxide. Subsequent reduction of 704 gave 705 (76JPR835). Hydrazone 703 was prepared by condensation of 4-hydrazino-3-nitropyridine with 702. The mass spectral fragmentation patterns for 704 and 705 and their benzo analogues were studied (77ZC142). 

From Hydrazones and Thionyl Chloride [4+1] Atom Fragments 479... 

Fragmentation of a,P-epoxyketones via the intermediacy of a,P-epoxy sulfonyl-hydrazones. 

In this ESI-FTMS screening proof-of-concept experiment, a DCL was generated using the hydrazone exchange reaction from two hydrazide fragments (1 and 2) and five aldehyde fragments (A-E) (Scheme 7.2). 

Scheme 7.2 Dynamic combinatorial chemistry targeting carbonic anhydrase. (a) Fragments for hydrazone exchange, (b) Dynamic combinatorial library generation.

Hydrazide 1 was designed as the CA anchor fragment and hence necessitated dual functionality an Ar-SO NH moiety for reliable CA affinity and a hydrazide moiety to take part in hydrazone exchange. Hydrazide 2 lacked the sulfonamide moiety of 1, but was still able to participate in hydrazone exchange and thus functioned as a control compound. Fragments A-E, the exchange partners for 1 and 2, were selected to introduce an array of tails onto 1 to enable exploration of periphery recognition interactions with CA. 

On the interaction of 1,3-diketones with dihydrazides of oxalic and malo-nic acids, the condensation products have been obtained in a molar ratio of 2 1 (88ZOR1823). In the solid state, they exist as the bispyrazolines 77 but in solution, equilibria are observed. These equilibria occur with the participation of the bispyrazoline tautomer, involving two diastereomers, and also of tautomers containing hydrazone and/or enhydrazine fragments. 

The carbonyl ylide precursor can be generated by lead tetraacetate oxidation of the hydrazone 58. Thermolysis of 59 in the presence of perdeuterated acetone led to a variety of products, some of which are shown above. An internal quench of the ylide via a 1,4-proton migration led to enol ether 61, while cycloaddition with perdeuterated acetone formed the dioxolane 62 and its regioisomer. Interestingly, the presence of products such as acetone and propene-t/s are proposed to indicate a reversible fragmentation of the ylide to a carbonyl derivative and a carbene. 

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