Atoms reaction with methylene groups

Mechanistic insight into this process was obtained by administration of labeled trideca- or undeca-3,6,9-trienoic acid instead of the natural C12 precursor (Figure 2). In this case, the artificial 2H metabolites can be analyzed by mass spectrometry without interference from the plants own 1H metabolites, since a homo- or norectocarpene is formed. The sequence of the oxidative decarboxylation/cyclization reaction proceeds without loss of 2H atoms from the double bonds but with loss of a single 2H atom from certain methylene groups of the precursor acids (Figure 3). If C(l) and a 2H atom from C(5) of the labeled precursor is lost, finavarrene is the product of the reaction channel. If the methylene group... 

The starting material was prepared with the modification on the epibatidine bicychc ring system by repositioning the nitrogen atom to a methylene group. We carried out the Hetero-Diels Alder reaction of cyclopentadiene and iminium ion generated from ammonium chloride and formaldehyde in the aqueous medium and protected resulted unstable secondary amine with benzoyl chloride to provide (3) in good yields [5] (Scheme 38.1). 

The Tebbe reagent functions as a nucleophilic carbenoid in its reactions with carbonyl groups. The carbenoid is activated in the presence of a Lewis base which presumably complexes with the aluminum atom. Tetrahydrofuran is the Lewis base in the reactions described above. If the reaction is performed in the absence of added tetrahydrofuran, the carbonyl oxygen atom can function as a weak Lewis base, although the methylenation process is considerably slower. 

Both hydrogen atoms of the methylene group originate from DMSO if the reaction is carried out with DMSO-dj, the resulting acetals have a CD2 unit. 

It is interesting to compare the alkenes formed in the reactions of 0( P) with 1-iodobutane and 2-iodobutane. In the reaction of O atoms with 1-iodobutane only one aUcene can be formed, namely 1-butene, and this is observed with a yield of around 70%. In the case of 2-iodobtane, however, there is the possibility of the formation of both 1-butene and cisitrans -2-butene as the major alkene product (see Figure 11). The measurements show that the major alkene is 1-butene with a yield of around 46%. This results implies that adduct formation of the O atom between the I atom and the terminal methyl group is favoured over adduct formation between the O atom and the methylene group. Formation of trans-2-butene was observed, however, the yield was difficult to quantify and only a limit of <10% can be set at present. 

The anion of phenol, in tautomeric form with the negative charge in the nucleus, attacks the carbon atom of the methylene group in the labile methylene diamine formed in reaction 15.5. 

Bromine Carriers. Z gler and Spaith showed that a hydrogen atom on a methylene group adjacent to an ethylenic double bond may be easily replaced with bromine by means of N-bromosuccinimide. This reaction proceeds by a free radical chain mechanism, and substitution may occur on either side of the double bond,... 

As seen from Table 11, the kinetically controlled products of the reaction between the methyl-substituted cations 545 and 547 are mainly tertiary, rather than secondary, acetates but in every case the products have only a cis-configuration. Upon acetolysis of 6,6-dideuterated monomethyl-substituted cis-tosylate 544 the tertiary acetate contains, judging by the PMR spectra, two H atoms in the methylene group of the cyclopropane ring, and the secondary — one H atom on the average, in full conformity with the structure of the intermediate ion 545. On the other hand, the secondary acetate formed on solvolysis of the trans-epimer contains two D atoms in the cyclopropane group. Thus in this case, either, no conversion is observed of a classical ion into a nonclassical one in the trans-epimer solvolysis. 

There are quite a few examples, discussed in the literature [72, 73, 80], of inversion of configuration in the Se2 reactions. In particular, an inversion of the bond configuration was registered in prochiral carbon atoms of the methylene groups of alkyl lithium tetramers (ROH2Li)4 in solution [82]. This result is consistent with the data of Table 5.3 which show preferability of the D31, form of CHjLij. 

Figure 2.9 Oxidation of an alcohol with NAD, and its reverse reaction, reduction of an aldehyde or ketone. B represents some basic group on the enzyme. The subscripts R and S are a means of distinguishing between the two hydrogen atoms of the methylene group, see the section on chirality at the end of this chapter...

Drying nonconjugated acids involves the formation of hydroperoxide groups on the allylic carbons, i.e., carbon atoms of the methylene groups adjacent to the double bonds. Polymerization occurs via a radical chain mechanism, called autoxidation. This theory also applies to conjugated acids, such as linolenates, but the drying reaction is much faster with these polyunsaturated oils. 

The large sulfur atom is a preferred reaction site in synthetic intermediates to introduce chirality into a carbon compound. Thermal equilibrations of chiral sulfoxides are slow, and parbanions with lithium or sodium as counterions on a chiral carbon atom adjacent to a sulfoxide group maintain their chirality. The benzylic proton of chiral sulfoxides is removed stereoselectively by strong bases. The largest groups prefer the anti conformation, e.g. phenyl and oxygen in the first example, phenyl and rert-butyl in the second. Deprotonation occurs at the methylene group on the least hindered site adjacent to the unshared electron pair of the sulfur atom (R.R. Fraser, 1972 F. Montanari, 1975). 

Reactions at G-5. The C-5 atom of hydantoins can be considered as an active methylene group, and therefore is a suitable position for base-cataly2ed condensation reactions with aldehydes (44). 2-Thiohydantoins give the reaction more readily than their oxygen counterparts ... 

If the dye contains no mobile substituents ia the chain, nucleophiles attack primarily the end carbon atoms (changing of terminal residues). Streptocyanines can be hydroly2ed ia aqueous alkaline solution to form the corresponding merocyanines and then the oxonoles (71,72). These processes are reversible. Nucleophilic reactions with the methylene bases of the corresponding heterocycles result ia polymethines containing new end groups (Fig. 

With active methylene compounds, the carbanion substitutes for the hydroxyl group of aHyl alcohol (17,20). Reaction of aHyl alcohol with acetylacetone at 85°C for 3 h yields 70% monoaHyl compound and 26% diaHyl compound. Malonic acid ester in which the hydrogen atom of its active methylene is substituted by A/-acetyl, undergoes the same substitution reaction with aHyl alcohol and subsequendy yields a-amino acid by decarboxylation (21). 

MSC undergoes reactions with alcohols, amines, active methylene compounds (in the presence of bases), and aromatic hydrocarbons (in the presence of Friedel-Crafts catalysts) to replace, generally, a hydrogen atom by a methanesulfonyl group (382—401). 

In general, reaction of diazomethane with a, -unsaturated carbonyl compounds affords pyrazolines in which the nucleophilic methylene group is attached to the carbon atom of the carbonyl compound. According to Huisgen, the reactions belong to the general class of 1,3-dipolar cycloadditions. 

The apparently loose structural requirements for antihista-iiiinic agents have already been alluded to. Thus, active compounds. ire obtained almost regardless of the nature of the atom that connects the side chain with the benzhydryl moiety. In fact, a methylene group, too, can also serve as the bridging group. Reaction of the aminoester, 95 (obtained by Michael addition of... 

---