3644-93-7

-

Sm11-intermediates generated upon addition of (Me2N)3P to a solution of SmI2 in THF exhibit the properties of a single-electron reducing agent and an N-nucleophile. In particular, N,N-dimethylamides are formed from esters.

The product comprises at least two diamide compounds selected from the diamide compounds of following formulae (Ia), (Ib), and (Ic): [in-line-formulae]R2R3NOC-Aa-CONR4R5??(Ia)[/in-line-formulae] [in-line-formulae]R2R3NOC-Ab-CONR4R5??(Ib)[/in-line-formulae] [in-line-formulae]R2R3NOC-Ac-CONR4R5??(Ic)[/in-line-formulae] wherein: R2, R3, R4, and R5, either identical or different, are groups selected from saturated or unsaturated, linear or branched, optionally cyclic, optionally aromatic, optionally substituted, hydrocarbon groups comprising an average number of carbon atoms ranging from 1 to 36, R2 and R3 on the one hand and R4 and R5 on the other hand may optionally form together a ring, optionally substituted and/or optionally comprising a heteroatom, andAa, Ab, and Ac are linear divalent alkyl groups, each comprising a different number of carbon atoms.

The reactions of the silyllithium reagent with tertiary amides was discussed. The enediamines were easily isomerized from cis to trans, easily oxidized to dienediamines and were hydrolyzed to α-aminoketones. If the two equivalents of the silyllithium reagent were used, the product was an α-silylamine. The results show that each member of the homologous series of amides gives rise to a substantially different product.

We have studied intramolecular hydrogen bonding in a homologous series of diamides (compounds 1-6) in methylene chloride, 9:1 carbon tetrachloride/benzene, and acetonitrile. By correlating variable-temperature 1H NMR and IR measurements, we have shown that the temperature dependence of the amide proton NMR chemical shift (Δδ/ΔT) can provide qualitative (and in some cases quantitative) information on the thermodynamic relationship between the intramolecularly hydrogen bonded and non-hydrogen-bonded states of flexible molecules. Among the hydrogen-bonded ring sizes represented in the diamide series, the intramolecular interaction is particularly enthalpically favorable in the nine-membered hydrogen-bonded ring (compound 4). Variable-temperature IR and NMR data indicate that the internally hydrogen bonded state of diamide 4 is 1.4-1.6 kcal/mol more favorable enthalpically than the non-hydrogen-bonded state, in methylene chloride solution; the non-hydrogen-bonded state is 6.8-8.3 eu more favorable entropically in this solvent. In contrast, there appear to be much smaller enthalpy differences between the internally hydrogen bonded and non-hydrogen-bonded states of diamides 2 and 3. Our findings are important methodologically because the temperature dependences of amide proton chemical shifts are commonly used to elucidate peptide conformation in solution. Our results show that previous "rules" for the interpretation of such data are incomplete. In non-hydrogen-bonding solvents, small amide proton Δδ/ΔT values have been taken to mean that the proton is either entirely free of hydrogen bonding or completely locked in an intramolecular hydrogen bond over the temperature range studied. We demonstrate that an amide proton can be equilibrating between intramolecularly hydrogen bonded and non-hydrogen-bonded states and still manifest a small chemical shift temperature dependence (implying that the hydrogen-bonded and non-hydrogen-bonded states are of similar enthalpy).