2-methyl Open-Chain Compound

Both of these structures are open-chained compounds corresponding to crown ethers in function if not exactly in structure (see Chap. 7). They have repeating ethyleneoxy side-chains generally terminated in a methyl group. Montanari and co-workers introduced the polypodes 22 as phase transfer catalysts . These compounds were based on the triazine nucleus as illustrated below. The first octopus molecule (23) was prepared by Vogtle and Weber and is shown below. The implication of the name is that the compound is multiarmed and not specifically that it has eight such side-chains. Related molecules have recently been prepared by Hyatt and the name octopus adopted. For further information on this group of compounds and for examples of structures, refer to the discussion and tables in Chap. 7. 

Perkin pointed out that open chain compounds, which are analogous in structure to a terpene, show a certain similarity in behaviour thus the addition of an ethyl group to 2-methyl 1 5-hexadiene by converting it into 2-methyl 3-ethyl 1 5-hexadiene changes the unpleasant acrid odour into a pleasant one reminding of lemon and peppermint. 

N-Benzoyl-Lalanine methyl ester is in turn about eight times more reactive than is its D enantiomer). The open-chain compounds may not bind to the enzyme in the same manner, however, as does the locked substrate. The conformation around the amido bond of the open-chain compounds, for example, can be transoid rather than cisoid (81). In addition, if equatorial 24 is considered to be the reactive conformer for both the Dand L enantiomers, and if the alanine methyl group is attracted to the hydrophobic aromatic binding subsite, then structures 34 and 38 would result. The L enantiomer of N-benzoyl-phenylalanine methyl ester 38 in this representation has approximately the same conformation as equatorial L-24. But attraction of the methyl of the D enantiomer to the location occupied by the methyl group of the L enantiomer causes the carbomethoxy group to move from the position it occupies in D-24. 

Dermer and Durr44 published in 1954 an interesting paper describing the reaction between ethylene oxide and formaldehyde di-methyl cetal in the presenoe of catalytic amounts of boron triflucride etherate. There wore isolated two open-chain compounds, in addition... 

The iV-acylated derivatives of maleic hydrazide, prepared from open-chain compounds, have been found to differ from acylated products obtained from maleic hydrazide acylations. Acylation of 4- or 5-substituted maleic hydrazides should permit the existence of two 0-acylated isomers. So far, only one isomer of unknown structure has been isolated from benzoylation of the 4-methyl analog. Maleic hydrazide and its 2-substituted analogs are 0-acylated with acetic anhydride, acyl halides, and 0,0-dialkylphosphorochlor-... 

Treatment of the A -l,2-oxaphospholen (100 R ==OMe) with LiBr in MeOH yields the salt (101) together with the open-chain compounds (102) and (103) in the proportions 1 1 2. The formation of (102), and particularly the high yield of (103), has been advanced as good evidence for the participation of the intermediate (104), from which transfer of axial methyl group to Br occurs. ... 

A novel transformation in aqueous alkali has been observed with 1-p-D-arabinofuranosyl-5-fluoro-uracil as outlined.3 The open chain compound was isolated in 50% yield and by treatment with diazomethane and then with alkali generated 1-p-D-arabino-furanosyl-3-methyl-5-... 

The Z-acid 256 was made from a lactone. Dehydration of the tertiary alcohol in the open chain compound 258 would give the C-alkene but after cyclisation to the lactone 259 dehydration with polyphosphoric acid (PPA) must give Z-260. Careful hydrolysis and methylation gives Z-261, the methyl ester of Z-261. 

The deaminations of fra 5-2-phenyl- and frans-2-methyl-cyclopropylamine hydrochlorides in acetic acid solution have been examined. The relative amounts of the various products are shown in (26)-(29) and (30)-(33), respectively. The most remarkable feature of these results is the formation of considerable quantities of ring-opened chlorides, which are scarcely formed in deaminations of related open-chain compounds. The addition of chloride ion led to a marked increase in the amount of chloride product. These and other results are interpreted in terms of the formation of a cyclopropyl-diazonium-chloride tight ion pair. The reactions were successfully modelled by ab initio calculations at the B3LYP/6-31G level, including a reaction-field solvent-effect calculation using the dielectric constant of acetic acid. 

Likewise, the reference structure (the open chain compound) may also be formed by the union of these two radicals (Fig. 2.6(b)). For this purpose, the methyl radical may be regarded as a simple case of an odd AH radical, the electron being in a normalized atomic orbital of energy ot and with a coefficient of unity. 

The salts of some enamines crystallize as hydrates. In such cases it is possible that they are derived from either the tautomeric carbinolamine or the amino ketone forms. Amino ketone salts (93) ( = 5, 11) can serve as examples. The proton resonance spectra of 93 show that these salts exist in the open-chain forms in trifluoroacetic acid solution, rather than in the ring-closed forms (94, n = 5, 11). The spectrum of the 6-methylamino-l-phenylhexanone cation shows a multiplet at about 2.15 ppm for phenyl, a triplet for the N-methyl centered at 7.0 ppm and overlapped by signals for the methylene protons at about 8.2 ppm. The spectrum of 93 ( = 11) was similar. These assignments were confirmed by determination of the spectrum in deuterium oxide. Here the N-methyl group of 93 showed a sharp singlet at about 7.4 ppm since the splitting in —NDjMe was much reduced from that of the undeuterated compound. 

However, these authentic cyclic compounds are converted by acetic anhydride or methyl iodide into derivatives of the hypothetical amino-aldehyde form. Methylation gives first the cyclic methiodides (23a-b) and (24) which occur by the addition of a single molecule of methyl iodide in the presence of sodium hydroxide and excess methyl iodide these are converted into the open-chain quaternary methiodides (25a-b) and (26). Similar examples have been given by Garden and by Gensler and co-workers. ... 

As expected, heterocyclic enols and potential enols (i.e, compounds existing mainly in the CH form) behave toward diazomethane similarly to the open chain and isocyclic enols, i.e. they form enol methyl ethers by reactions of the SnI type (cf. footnote 29). Examples of this behavior are barbituric acid, picrolonic acid, dchydroacetic acid (64), 3-methyl-l-phenylpyrazolin-5-one, 1-phenylpyrazoli-dine-3,5-dione, 1,2-diphenylpyrazolidine-3,5-dionc, 3-hydroxy-... 

Reaction of hydrazine 165 with a number of monosaccharides give hydrazones 166 (92BCJ546). Their acetylations gave peracetyl derivatives 167. The same reactions were extended to the /V-methyl and the 7-methyl derivatives of 165 (93 JPROO). That compounds 166 exist as open-chain structures was based on a 2D NMR study (93MI1) (Scheme 35). 

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