Heterocycles Contenant du Phosphore—XII: Etude par Resonance Magnetique Nucleaire des Oxo- et Thio-2 Phenoxy-2 Trimethyl-3,5,5 Oxazaphosphorinanes-1,3,2. Un Cas Particulier de Systeme ABXY

After elimination of the P? H spin coupling, the PMR spectra of the title 1,3,2-oxazaphosphorinanes give rise to an ABXY pattern where J_AX = J_AY = J_BX = 0. The particular ABXY system where J_AY = J_BX = 0 is studied to calculate the expression of the E₇, E₈, E₉ and E₁₀ energy-levels and the frequency of the transitions connected to these energy-levels. The relative sign of the ³J_P? O? C? H and ³J_P? N? C? H coupling constants is given by INDOR experiments. The ring conformation is discussed.     

Les Amines Biogènes (Phénol- et Catéchol-Amines): Attribution des Spectres de Résonance 13C et Etude de la Deprotonation

A number of phenol- and catechol- amines has been studied in aqueous solutions at acidic and alkaline pD by means of ¹³C NMR. Resonance assignments are achieved for the fully protonated forms and the influence of the side chain on the aromatic carbons is studied. The shielding effects associated with the various types of side chain tend to follow an additive relationship. The pD dependence of the ring and side chain carbon resonances in phenolamines is accounted for by considering the sum of two separate and opposite effects related to ring and side chain deprotonations. Such a simple model fails to apply to the catechol derivatives. This difference is discussed in terms of the orientational dependence of the deprotonation shifts. It is shown that the protonated amino group is the less acidic group in phenol- and catechol-amines.     

Orientation in the 1,3-dipolar cycloaddition of diazomethane with alkylethylenes

The regiochemistry of diazomethane cycloadditions with simple alkylethylenes, heretofore not reported, was investigated in the simplest case, diazomethane and propene. The products were 3-and 4-methylpyrazolines in 7.4/1 ratio, in accord with the diradical mechanism. This mechanism also accounts for the abnormal orientation in intramolecular cases and with bridgehead olefins.     

The fixed conformation of the leucyl side-chain in a tripeptide

The complete analysis of the ¹H NMR spectrum of the leucyl side-chain of a tripeptide allows the deduction of the conformation of this side-chain. In the peptide, in contrast to the free amino acid, the side-chain is in a single fixed conformation.     

The first regioselective metalation and functionalization of unprotected 4-halobenzoic acids

[reaction: see text] By treatment with s-BuLi, s-BuLi/TMEDA, or t-BuLi at approximately -78 degrees C, 4-fluoro- and 4-chlorobenzoic acids (1a,b) are metalated preferentially in the position adjacent to the carboxylate. A complete reversal in regioselectivity is observed for 1a when treated with LTMP; a sequential process involving a rapid intraaggregate lithiation through a quasi dianion complex "QUADAC" is postulated to explain the unusual reactivity of Me(2)S(2) and I(2).