Lactam Complexes Research Articles

A Protic Mn(I) Complex Based on a Naphthyridine-N-oxide Scaffold: Protonation/Deprotonation Studies and Catalytic Applications for Alkylation of Ketones

A Mn(I) complex (1) bearing a proton responsive hydroxy unit on 1,8-naphthyridine-N-oxide scaffold (L1H) was synthesized. The molecular structure of 1 revealed the lactim form of the ligand. The corresponding deprotonated lactam complexes [18-C-6-K·2] and 3 were prepared and structurally characterized. The acid–base equilibrium between the lactim and lactam forms was studied by 1H NMR and UV–vis spectra. The catalytic efficiency of 1 was evaluated by performing α-alkylation reaction of ketones with primary alcohols. The scope of the α-alkylation reaction is broad in terms of both ketones and alcohols. The efficacy of the protic catalyst is demonstrated in the alkylation of the bioactive steroids progesterone and pregnenolone. A controlled catalyst [Mn(L2)(CO)3Br] (4), which is structurally similar to 1 but devoid of the proton responsive hydroxy unit, shows significantly reduced catalytic efficiency validating the crucial role of the hydroxy functionality in 1. Kinetic study, control reactions, and deuterium labeling experiments were conducted to gain mechanistic insights.

1,7-Induction of chirality in Mukaiyama aldol reactions using π-allyltricarbonyliron lactone and lactam complexes as chiral templates

The Mukaiyama aldol reactions of silyl enol ether-substituted π-allyltricarbonyliron lactone and lactam complexes with aldehydes under BF 3.OEt 2 activation proceed with moderate to excellent diastereocontrol. The level of diastereocontrol is strongly affected by the nature of the endo substituent on the complex, seven carbon atoms distant from the reaction site. A detailed investigation of the reaction is presented and a model for the observed stereoselectivity proposed.

ChemInform Abstract: A New Route to Functionalized π‐Allyltricarbonyliron Lactam Complexes from Aziridines and Their Use in Stereoselective Synthesis and Oxidative Conversion to β‐Lactams.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Mukaiyama aldol reactions of π-allyltricarbonyliron lactone and lactam complexes bearing trimethylsilyl enol ether side-chains. Not just formal, but genuine 1,7 induction of chirality

A comparison of diastereoselectivities in the Mukaiyama aldol reactions of three types of trimethylsilyl enol ether substituted iron carbonyl complexes has provided evidence for the stereodirecting effect of remote substituents in π-allyltricarbonyliron lactone and lactam complexes.

A new route to functionalised π-allyltricarbonyliron lactam complexes from aziridines and their use in stereoselective synthesis and oxidative conversion to β-lactams

Aziridinyl enones can be converted in good yield into π-allyltricarbonyliron lactam complexes bearing ketone functionality in the side chain; addition of a variety of nucleophiles into the side chains of these complexes proceeds in good yield and excellent (>95%) de to afford secondary and tertiary alcohols which on treatment with trimethylamine N-oxide form the corresponding β-lactams in good yield.

Ultrasound in synthesis: natural products and supersonic reactions?

Sonochemical syntheses of a number of useful reagents such as samarium diiodide, sodium phenylselenide, tertiary alkoxides and the reducing agent [(PPh 3P)CuH] 6 are discussed. The rates of these sonochemical reactions can be increased by the addition of electron-transfer agents, such as benzophenone ketyls. These results would not be expected on the basis of mechanical effects alone and lend support to proposals that ultrasound acts preferentially on single electron-transfer processes. Ultrasound also allows the rapid and efficient generation of tetracarbonyliron, which can be trapped by simple organic compounds, such as conjugated dienes, vinyl epoxides and allylic alcohols. In the latter cases, this allows the facile preparation of π-allyltricarbonyliron lactone and lactam complexes that can be converted to give a range of biologically active β-, γ- and δ-lactones, including a number of alkaloids and antibiotics. In addition, the δ-lactone products have been incorporated into several complex multi-step syntheses of macrocyclic natural products. The synthesis of key fragments of the potent antiparasitic agent avermectin B1a demonstrates that the sonochemical reaction conditions are fully compatible with the synthesis of highly functionalized molecules.

Tricarbonyliron lactone complexes in organic synthesis

Abstract

ChemInform Abstract: Organic Synthesis with Tricarbonyliron Lactone Complexes

π-Ally tricarbonyliron lactone complexes are useful precursors for organic synthesis. These stable complexes are readily prepared from a variety of organic substrates and may be respectively converted to β- and δ-lactones by selective oxidation or exhaustive carbonylation. The natural products massoialactone, parasorbic acid, the carpenter bee pheromone and malyngolide were prepared by using the iron carbonyl methodology, along with precursors for the ionophore antibiotic CP 61405 and avermectin B1a synthesis. Several corresponding lactam complexes were obtained by treatm ent of the π-allytricarbonyliron lactones with amines in the presence of Lewis acids. These complexes were used in the formal total synthesis of the nocardicins and ( + )-thienamycin.

Organic synthesis with tricarbonyliron lactone complexes

π-Ally tricarbonyliron lactone complexes are useful precursors for organic synthesis. These stable complexes are readily prepared from a variety of organic substrates and may be respectively converted to β- and δ-lactones by selective oxidation or exhaustive carbonylation. The natural products massoialactone, parasorbic acid, the carpenter bee pheromone and malyngolide were prepared by using the iron carbonyl methodology, along with precursors for the ionophore antibiotic CP 61405 and avermectin B1a synthesis. Several corresponding lactam complexes were obtained by treatm ent of the π-allytricarbonyliron lactones with amines in the presence of Lewis acids. These complexes were used in the formal total synthesis of the nocardicins and ( + )-thienamycin.

Synthesis of the β-lactam antibiotic (+)- thienamycin via an intermediate π-allyltricarbonyliron lactone complex

The π-allyltricarbonyliron lactone complex ( 7), formed by reaction of E-1,2-epoxy-2-methyl-6,6-dimethoxyhex-3-ene( 5) with co-ordinatively unsaturated iron carbonyl species, was reacted with benzylamine to give a lactam complex ( 8) by an S N'-like mechanism. This complex upon oxidation with Ce( IV) afforded cis-3-isopropenyl-4-[(2',2'-dim ( 9) which was chemically modified into trans-3-(1'-hydroxyethyl)-4-[(2',2-dimethoxy)ethyl] azetidin-2-one ( 13), a key intermediate previously used in the synthesis of the antibiotic thienamycin. Similar reaction with ( S)-(-)-α-methylbenzylamine afforded a separable mixture of diastereoisomeric iron lactam complexes ( 16 and 17). These complexes could be individually converted to the corresponding optically active β-lactam derivatives ( 27 and 28) and, hence, are precursors for the synthesis of either natural (+)-thienamycin or unnatural (-)-thienamycin.

Use of π-allyltricarbonyliron lactam complexes in the preparation of nocardicin derivatives: synthesis of (–)-3-oxo-1-[(p-benzyloxyphenyl)-benzyloxycarbonylmethyl]azetidin-2-one

A short five-step synthesis, in 79% overall yield, of (–)-3-Oxo-1 -[(p-benzyloxyphenyl) benzyloxy-carbonylmethyl]azetidin-2-one (3), a precursor for nocardicin synthesis has been developed from isoprene monoepoxide. The key steps of the procedure rely on the efficient transformation of 2–4-η3-(1-formyloxy-2-methylbut-3-en-2-ylato)tricarbonyliron into the corresponding diastereoisomeric lactam complexes (6) and (7) using D-(–)-benzyl-(p-benzyloxyphenyl)glycinate (5) and ZnCl2·TMEDA (TMEDA = tetramethylethylenediamine), and their oxidation with ceric ammonium nitrate to 3-isopropenylazetidinone derivatives.

Synthesis of β-lactams from π-allyltricarbonyliron (lactone) complexes

Several π-allyltricarbonyliron (lactone) complexes have been treated with an excess of benzylamine in the presence of Lewis acids to afford the corresponding lactam complexes by an SN2′-like process. These lactam complexes were oxidised in good yield with ceric ammonium nitrate to provide a novel route to a variety of β-lactam compounds. Simple chemical transformations of the resulting β-lactams have been investigated; these include the conversion of the vinyl and isopropenyl side chains into hydroxyethyl substituents and the reductive removal of benzyl groups to afford the parent NH β-lactams.

ChemInform Abstract: FORMATION OF β‐LACTAMS FROM TRICARBONYLIRON LACTONE COMPLEXES

AbstractDurch Umsetzung der Tricarbonyleisenlacton‐Komplexe (I) mit Benzylamin (II) entstehen die Tricarbonyleisenlactam‐Komplexe (III), die mit Cerammoniumnitrat (CAN) zu den Lactamen (IV) bzw. (V) und (VI) oxidiert werden.

Formation of β-lactams from tricarbonyliron lactone complexes

A number of tricarbonyliron lactam complexes were prepared from the corresponding lactone complexes by reaction with amines in the presence of ZnCl2 and on subsequent oxidation with CeIV gave β-lactams in excellent yield.

The chemistry of uranium—IX

Abstract Lactam complexes of thorium and uranium tetrahalides, ThCl4(aco)4. acetone, ThI4. 8L, UCl4 . 4L, UBr4(pip)6, UBr2(pip)6(ClO4)2 and UI4 . 8L, where L is 2-piperidone (pip), 1-aza-cyclooctan-2-one(aco) and ϵ-caprolactam (cl) have been isolated. These compounds were characterized by spectroscopic and magnetic susceptibility measurements. The various equilibria resulting from the interactions of uranium(IV), halide, solvent and 2-piperidone were studied by conductometric and spectrophotometric methods. These indicated that eight coordinated uranium(IV) complexes crystallized out of solutions containing a large amount of octahedral uranium(IV).