Oxygenated monoterpenes as dipolarophiles for nitrilimine cycloadditions

A variety of naturally-occurring oxygenated monoterpenes, namely (S)-cis-verbenol, (1R)-(-)-myternol, (1S)-(-)-verbenone, (1R)-(-)-myternal, (S)-(-)-perillyl alcohol, and (S)-(-)-perillaldehyde have been submitted to nitrilimine cycloaddition. These processes were fully regio- and stereoselective for four dipolarophiles. In contrast, regioselective but non-stereoselective cycloadditions occurred in the case of two of the monoterpene derivatives. The configurations of the newly-formed stereocentres of the cycloadducts were assigned on the basis of NOE and NOESY experiments

Stereoselective intramolecular cycloadditions of homochiral nitrilimines: synthesis of enantiopure (6S)-substituted-2,3,3a,4,5,6-hexahydro-furo[3,4-c]pyrazoles

Starting from (S)-ethyl lactate and (S)-ethyl mandelate the homochiral hydrazonoyl chlorides 4b-d have been synthesised. Their base treatment promoted the in situ generation of the corresponding nitrilimines 5b-d, which gave the enantiopure title compounds with good overall yields and diastereoselectivities

15N NMR spectroscopy of partially unsaturated pyrazoles

Partially saturated pyrazoles, namely 1-(4-substituted)phenyl-3-methoxycarbonyl-5-ethoxycarbonyl-4,5-dihydropyrazoles, were submitted to extensive 15N NMR spectroscopic analyses, performed in natural abundance. Nitrogen chemical shifts were measured by means of INEPT and HMBC experiments, while long range proton\u2013nitrogen scalar coupling values were taken through J-HMBC experiments. A linear plot between nitrogen chemical shifts and Hammett \u3c3p was observed, enabling us to relate quantitatively the observed chemical shifts to the electronic features of the substituent in the 1-position of the 4,5-dihydropyrazole ring

15N NMR Spectroscopy of Annulated \u3942- Pyrazolines and \u3942-1,2,4-Triazolines

Enantiopure \u3942-pyrazolines and \u3942-1,2,4-triazolines fused to the 1,4-benzodiazepine moiety, as well as \u3942-pyrazolines annulated to the 1,5-benzoxazocine moiety (racemic) or inserted in a bis-1,3-pyrazolophane skeleton (enantiopure) were investigated through 15N NMR spectroscopy in natural abundance. Nitrogen chemical shifts were determined by (1D)-INEPT experiments, while proton-nitrogen scalar coupling were obtained through 2D-J-HMBC experiments

Stereoselective intramolecular cycloadditions of homochiral nitrilimines as a source of enantiopure 2,3,3a,4,5,6-hexahydro-pyrrolo[3,4-c]pyrazoles

Abstract: Starting from the methyl esters of glycine, L-alanine, L-phenylalanine and (S)-2-phenylglycine, we developed a synthetic route to the title compounds in the enantiopure form by means of a stereoselective intramolecular 1,3-dipolar cycloaddition of homochiral nitrilimines 5a-d. Fair to good overall product yields and high cycloaddition diastereoselectivity were obtained