Stereochemical Aspects of a Two-Step Staudinger Reaction − Asymmetric Synthesis of Chiral Azetidine-2-ones

Abstract

Reaction of N‐trialkylsilylimines with a variety of glycine‐derived ketenes produced 1,3‐azadienes, which in some cases have been isolated and characterised. A conrotatory ring closure of these compounds gave rise to the formation of the azetidine‐2‐ones, thus allowing a formal two‐step Staudinger reaction. Exclusive trans diastereoselectivity was observed. A less stringent diastereofacial selectivity was obtained. A set of experiments has been performed in order to evaluate the influence of the structural parameters as well as reaction conditions. Ab initio studies at MP2/6−31G* and QCISD(T)/6−311G** levels on model compounds provide a rationalization of the experimental results obtained. From the experimental as well as theoretical data it is clear that the presence of the silyl enol group in the intermediate azadiene is crucial in its stabilisation and plays a fundamental role in the conrotatory ring closure and, therefore, in the formation of the azetidine‐2‐one ring.

Synthesis, Spectral Correlations and Biological Activities of Some (E)-[4-(Substituted Benzylidene Amino)Phenyl] (Phenyl) Methanones

“…The proton chemical shift ( ppm) with Hammett ,  + ,  R , F and R constants is satisfactorily. The remaining Hammett constant  I were found to be fail with positive  values except  I and F excluding 3-Br, 2-CH 3 . This shows that the normal substituent effect operates in all system.…”

“…Many Schiff's bases are known to be medicinally important and are used to design medicinal compounds [2]. They are well known intermediated for the preparation of azetidinone [3], thiazolidinone [4], formazone [5], arylacetamide [6], metal complexes [7][8][9] and many other derivatives [10][11]. Many reagent have been used for the synthesis of optically active imines such as Lewis acids [12], MnO 2 [13], CaO [14], ZnCl 2 [15], P 2 O 5 :SiO 2 [16], infrared [17], ultrasound radiation [18] and fly-ash:H 2 SO 4 [19] with microwave irradiation.…”

Synthesis, Spectral Correlations and Biological Evaluation of Some Aryl (E)-N-Benzylidene-3-nitrobenzenamines

“…Benzylidene anilines belong to a class of compound called aldimines, which are the condensed products of aldehydes or ketones with primary amines and have azomethine group (CH=N) as the characteristics functional moiety. Interests in these compounds are largely due to their structural similarities with natural biological substances and relatively simple procedures of synthesis as well as synthetic flexibility that enable the design of suitable structural properties (Patai 2009;Jungreis et al, 1969).They are well known intermediate for the preparation of azetidinone (Bongini et al, 2000), thiazolidinone (Mulwad et al, 2002), formazone (Weber et al, 2005), arylacetamide (Fukumura 2008), metal complexes (Singh 2007;Zhu et al, 2008;Zhu et al, 2009) and many other derivatives (Wang et al, 2008;Cheng et al, 2009). …”

Application of the Octacarbonyldicobalt‐Catalyzed Carbonylation of Ethyl Diazoacetate for the One‐Pot Synthesis of N‐tert‐Butyl‐trans‐α‐ethoxycarbonyl‐β‐phenyl‐β‐lactam

“…The existence of a zwitterionic intermediate would suggest that the stabilization energy of the solvent plays an important role, especially if the inward–outward energy difference of the intermediates and transition‐state structures are small 13. Other studies have shown, however, that the introduction of solvation did not influence the diastereoselectivity or the overall reaction energetics 14…”