Halides homologization

Examination of plots of the enthalpies of formation of the various halide homologous series in the gaseous or liquid phase versus the number of carbon atoms immediately reveals at least two features. First, the enthalpy of formation of the methyl halide23 in any monohalogenated -alkyl series deviates from the otherwise apparently linear relationship established by the higher members of the series. This methyl effect is well-known2,24 and is dependent on specific interactions of adjacent nonbonded atoms which become... 

Because the enthalpies of formation of each halide homologous series correlate with the number of carbon atoms according to equation 1, the enthalpies of formation of any one series must correlate with the enthalpies of formation of any other series34 with like nc, as in equation 3. 

Several syntheses of l,3-dioxoperhydropyrrolo[l,2-c]imidazoles have been developed using different strategies. a-Substituted bicyclic proline hydantoins were prepared by alkylation of aldimines 135 of resin-bound amino acids with a,tu-dihaloalkanes and intramolecular displacement of the halide to generate cr-substituted prolines 136 and homologs (Scheme 18). After formation of resin-bound ureas 137 by reaction of these sterically hindered secondary amines with isocyanates, base-catalyzed cyclization/cleavage yielded the desired hydantoin products <2005TL3131>. 

This homologation of an oxime ether may have wider application for coupling of alkyl halides to other substrates such as acrylic esters (equation II). 

Radical homologation. This tin pinacolate is known to generate trimethyltin radicals at 60° and appears to be superior to tributyltin hydride as a source of stannyl radicals for addition of alkyl halides to O-benzylformaldoxime (equation I).1 Iodides, bromides, and selenides can be used as radical precursors. The same... 

Some synthetically important allenylmetallics, such as allenylzinc and allenylin-dium reagents, are prepared from allenylpalladium intermediates. These reactions are discussed in appropriate sections of this chapter. This section covers the reactions of allenylpalladium compounds without further transmetallation. Allenylpalladium complexes can be prepared from propargylic halides, acetates, carbonates, mesylates, alcohols and certain alkynes [83-87], The allenylpalladium compound prepared from 3-chloro-3-methyl-l-butyne has been isolated and characterized spectroscopically (Eq. 9.106) [83], It was found to couple with organozinc chlorides to produce homologated allenes quantitatively (Eq. 9.107). 

Hydroxylic solvents are capable of solvating anions through hydrogen bonding, and so halide mobilities are relatively low in alcohols, with chloride the least mobile. The mobility decreases observed for all the halides upon going up the homologous series of aliphatic alcohols may be the result of the increased size and mass of the alkyl group. A similar mass effect may be seen in the lowered mobility of the halides in dimethylacetamide compared to dimethylformamide. Here, as in the alcohol series, dipole moments and viscosities of the two solvents do not appear to be sufficiently different to explain the mobility differences. 

Formylation of an alkyl or aryl halide to the homologous aldehyde by transformation to the corresponding organometallic reagent then addition of DMF (M = Li, Mg, Na, and K). 

Since alkyl phenyl teUurides are easily prepared from alkyl hahdes and phenyltel-luromethyllithium, procedure C constitutes a homologation of alkyl halides. 

Other disulfanes can be prepared similarly, as summarized in Table IV. The yields are substantially higher when sulfenyl halides of the formula CFnCls-jjSX (X = Cl, Br) are reacted. Within a homologous series the... 

In 1990, Hahn and Tompkins reported an interesting multi-carbon homologation of alkyl halides by the reaction of magnesium carbenoid with a Grignard reagent (Scheme 2) . 

Benzodiazocines have attracted much interest as homologs of 1,4-benzodiazepine drugs, and several efficient cyclization methods have been developed. The diamine (289 R = H), available by several routes from the aminobenzophenone, cyclizes slowly in hot pyridine, but treatment of the halide (288) with ammonia leads directly to (292), perhaps by prior... 

---