Boron ring systems alternative

Cyclic species of equal numbers of alternating boron and nitrogen atoms may be considered as condensation products of monomeric B—N units and recent work by Paetzold 8-11> gives some credence to Wiberg s view that boronimides, XB=NR, are possible intermediates in the formation of cyclic B—N compounds. Boronimides may polymerize or may be trapped by 1,3-dipolar agents 8 11>. In similar fashion, the formation of the cyclotetrazenoborane ring system 1... 

Transannulation of the mesylate (33), derived from 4,8-dimethylcycloocta-4-en-l-ol, using sodium carbonate in aqueous dioxane has provided the bicyclo[3.3.0]octanol (34), a central precursor to the monoterpene iridomyrmecin (35 equation 13). In studies of the biomimetic synthesis of the natural tri-quinanes capnellene (37 equation 14) and pentalenene (40 equation IS) Pattenden et al. have shown that both molecules can be produced from appropriate cycloocta-l,S-diene precursors, i.e. (36) and (39) [or indeed their corresponding positional isomers (38) and (41), respectively] by treatment with boron trifluoride. Mehta et al. have described an alternative transannulation approach to the triquinane unit found in pentalenene, i.e. (42) - (43 equation 16), and also to the ring system (44 equation 17) found... 

Boroxines have trimeric, cyclic structures with planar rings of alternating boron and oxygen atoms. The alkyl groups are also in the plane of the ring. Boron can also be incorporated into numerous carbon ring systems. 

Several general methods are available for synthesizing systems with alternating boron and nitrogen atoms in the ring, but more specialized... 

While palladium(II) and copper(II) build solely 1,2-diolato complexes with erythritol which leads to five-membered chelate rings, boron(III) is involved in the six-membered rings as in the bis(phenylboronic acid ester) 13 (O Fig. 2). Erythritol adopts a zigzag conformation similar to that in 9 but the oxygen atoms are grouped alternatively on opposite sites of the C4-chain. The six-membered chelate rings in half-chair conformation provide a suitable bond pattern for a boron center involved in the delocalized jr-hond system of the phenyl suhstituent. 

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