Systems Containing Four-membered Rings

Volume IB Four-membered Rings, with all Fused Systems containing Four-membered Rings... 

IX. Systems Containing Four-membered Rings A. Cyclobutane... 

Intermolecular [2+2] photocycloaddition has been applied to the synthesis of a wide variety of natural products and their analogs, which frequently contain four-membered rings in highly ordered chiral environments, or a structure which can be readily derived from the [2+2] cycloadduct. The marine natural product Spatol (57) contains a three fused ring system (see Scheme 16). This has been... 

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 =... 

The [5,5] (2Nl)-fused heterocyclic system contains four ring-carbon atoms, the fusion carbon atom and two and one carbon atom in the respective five-membered rings. 

Some selected reactions of 21b were investigated [32]. In the reaction with [(Ph 0)4W=0j the dinuclear compound 24 is formed (Eq. 16) containing an almost planar W2OP four-membered ring system. The structure of 24 reveals that after the formal cycloaddition reaction a reductive W-W bond formation occurs under loss of OPh moieties. 

Penicillin and cephalosporin antibiotics are usually classed as P-lactam antibiotics, since their common feature is a lactam function in a four-membered ring, typically fused to another ring system. This second ring takes in the P-lactam nitrogen atom and also contains sulfur. In the case of penicillins, e.g. benzylpenicillin, the second ring is a thiazolidine, and in the cephalosporins, e.g. cephalosporin C, this ring is a dihydrothiazine. What is not readily apparent from these structures is that they are both modified tripeptides and their biosyntheses share a common tripeptide precursor. 

The boron-centred biradicaloid (R2PBR )2 (5.17, R = Pr, R = Bu) is an isoelectronic analogue of the (RPCR)2 biradicaloids, 5.14 and 5.15. Both of these four-membered rings contain 22 valence electrons for R=H. The P2B2 system 5.17 is synthesised by the reaction of a 1,2-dichlorodiborane with two equivalents of LiP Pr2. The P2B2 ring is presumably formed by rearrangement of the initially formed acyclic P-B-B-P skeleton (Scheme 5.2). 

A fascinating aspect of the chemistry of boron-chalcogen ring systems is the use of four-membered rings containing tin, (Tbt)B(p-E)2SnPh2 E = S, Se ... 

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