Four-membered ring systems

Departamento de Quimica Organica I. Facultad de Quimica. Universidad Complutense de 

Instituto de Quimica Organica General, CSIC, Juan de la Cierva 3, 28006-Madrid, Spain Palmendros iqog.csic.es 

The direct, stereoselective conversion of alkynes to A-sulfonylazetidin-2-imines 16 by the initial reaction of copper(l) acetylides with sulfonyl azides, followed, in situ, by the formal [2+2] cycloaddition of a postulated A-sulfonylketenimine intermediate with a range of imines has been described 06AG(E)3157 . The synthesis of A-alkylated 2-substituted azetidin-3-ones 17 based on a tandem nucleophilic substitution followed by intramolecular Michael reaction of primary amines with alkyl 5-bromo-4-oxopent-2-enoates has been 

Departamento de Quimica Orgdnica I. Facultad de Qutmica. Universidad Complutense de 

Strained four-membered heterocyoles have received considerable attention for a variety of reasons. In addition to being key scaffolds in natural products as well as in compounds of biological and industrial interest, the use of four-membered rings as starting materials to prepare many different substances provides the motivation to explore new chemistry based on these compounds. Oxygen- and nitrogen-containing heterocycles, in particular P-lactams, dominate the field in terms of the number of publications. This chapter covers selected relevant aspects in this area. 

A combined experimental and computational study of the photopreparation of fused 

4 additions to nitroalkenes and that the intermediates formed are highly reactive and undergo clean cyclization to azetidine oxime esters 12 05OL2643 . A practical 

A review on the synthesis of the carbopenam antibiotics has appeared. The l-azabicyclo[2.1.0]pentane skeleton has been reported this year, as is the first readily performed displacement of 4-acetoxyazetidinone with enolate anion equivalents. Most notable, however, is the preparation and utilization of a series of 1,2-diazetidinium ylides, which appear to have great potential in heterocyclic synthesis. The one missing cyclo-adduct of singlet oxygen and cycloheptatriene has now been described, as has the first, highly unstable, benzodithiet.  

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Lappert, M. F., and M. K. Majumdar The Three-coordinate Boron-Nitrogen Four-membered Ring System (l,3-Diaza-2,4-boretane). Proc. chem. Soc. [London] 1963, 88. 

These dilithium derivatives (2) react with SiF4 according to the substituents to give the four-membered ring systems 3 and 4 [1-3],... 

Unfortunately, both the lithium and the sodium compound are stable even when melted, destilled or sublimed. Therefore, Si-O four-membered ring systems are not accessible by this method of synthesis up to now. 

In contrast, Fe-Hg-X complexes show little tendency to form halide bridged species and less is known about complexes containing Zn. We first reported the formation of Fe-Si-O-M four membered ring systems with soft metals M = Ag, Rh, Pd, and Pt, and then prepared bimetallic complexes with more oxophilic metals in order to better understand the conditions for the occurrence of this unusual (t-alkoxy-silyl bridging mode. We have expanded our studies on Cd-containing complexes [3b-d] to Group 13 elements and we report here about the synthesis and reactivity of new, stable heterometallic Fe-M (M =... 

This unexpected expansion of the triafulvene skeleton to a four-membered ring system presents further evidence in support of the reaction scheme of triafulvenes toward ylides 427 suggested for cyclopropenones (p. 81). 

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