Boron-sulfur heterocycles

Few examples have been reported of metals coordinated to six-membered boron-sulfur heterocycles. Ashe et al. prepared 4-methyl-l,4-thiaborin (SC4H4BMe) which forms a stable molybdenum tricarbonyl sandwich complex 144.158 jn g etjert s laboratory, the reaction of the diborolyl complex 33 (Section 3.01.3.2) with COS afforded the dinuclear complex 145 whose structure was determined crystallographically.36 Other products, not involving boron-sulfur heterocycles and hence outside the scope of this discussion, were obtained via the treatment of 33 with different sulfur reagents such as CS2.36... 

The boron-sulfur heterocycles are analogous to the boron-oxygen heterocycles. These include 1,2-thiaborolanes 18, 2,5-dihydro-l,2-thiaboroles 19, 2,3-dihydro-l,2-thiaboroles 20, and 2,3-dihydro-l,2-benzothiaboroles 21. Deprotonation of 19 or 20 affords 1,2-thiaboratoles more commonly known as 1,2-thiaborolyl 22. Deprotonation of 21 gives 1,2-benzothiaboratole (1,2-benzothiaborolyl) 23. 1,2-phosphaborolanes 24 have been reported. 

Figure 10 Comparison of the Cand B NMR chemical shift values of analogous unsaturated boron-nitrogen, boron-oxygen, and boron-sulfur heterocycles. The spectra of 123,124 and 125 were recorded in THF-dg. All other spectra were recorded in benzene-de. n.o. means not observed.

Cyclic dimeric or tetrameric boron-nitrogen compounds can be prepared by the same route. Boron-sulfur heterocycles can be generated ... 

The reactions of 9-Cl-9-borabicyclo[3.3.1]nonane (9-C1-9-BBN) or 9-MeO-9-BBN with MeSCH2Li-(TMEDA) have been investigated, leading to the isolation of the unprecedented boron—sulfur heterocycles 117 and 118 (Scheme 39) (2014OM4336). The former product 117, an inner salt formally composed of sulfonium and borate subunits, rearranges... 

The chemistry of cyclic oligomeric and high polymeric phosphazenes is dominated by substitution reactions, as is the chemistry of boron-nitrogen heterocycles. However, substitutive techniques play only a minor role in the chemistry of siloxane, silazane, phosphate or metaborate oligomers and polymers. It is not yet well developed in sulfur-nitrogen systems but may become more important in the future. 

Boron, D. J. Atlas, R. M. Johnson, A. R., et ah, Method for removing organic sulfur from heterocyclic sulfur containing organic compounds. Patent No. USH1986H. 

Benzo-1,3-ditellurolylium tetrafluoroborate 76 turned out to be the first preparatively isolated salt of a heterocyclic carbocation containing two tellurium atoms in a ring (91UP3). The synthesis of 76 was carried out, similar to its sulfur analog benzo- 1,3-dithiolylium boron tetrafluoride (76BCJ3567), by treatment of a solution of 2-butoxybenzo-l,3-ditellurole in acetic anhydride with 2 equivalents of HBF4. 

A short time ago numerous triorganyl-cyclotriphosphanes have become accessible as pure substances on various synthetic routes (2). Moreover, three-membered phosphorus heterocycles with carbon, silicon, germanium, arsenic, boron, and sulfur as hetero ring atoms could be synthesized (2). Recently, we have found that such compounds with elements of the fifth periodtare als stable enough fop existence. Through the reaction of K(Bu )P-P(Bu )K with Bu S C1 or Bu -SnC at -78°C, the diphosphastib rane ... 

BORON-, SILICON-, PHOSPHORUS- AND SULFUR-CONTAINING HETEROCYCLES... 

Most importantly, the scope of the Diels-Alder reaction is very high - not only allowing the synthesis of cyclohexenes and 1,4-cyclohexadienes using 1,3-butadienes and alkenes and alkynes, respectively, but also giving access to a multitude of different heterocycles by exchanging the atoms a-d in the butadiene as well as the atoms e and f in the alkene by hetero atoms such as oxygen, nitrogen and sulfur. However, also dienes and dienophiles with several other atoms as phosphorous, boron, silicone, and selenium have been described. Thus, many different heterodienes and heterodienophiles have been developed over the years (Tables 1-1 and 1-2). 

Both acid and base catalysis have been used extensively to catalyze exchange in aromatic, and to a lesser extent, heterocyclic molecules. In acid exchange, the most widely used catalysts are sulfuric acid,122,129, 131 phosphoric acid,132 trifluoroacetic acid5133 perchloric acid,134 aluminum chloride,135 and the phosphoric acid-boron trifluoride complex.132 These reactions constitute the simplest electrophilic substitution. The mechanism for such substitution in benzenoid compounds is now comparatively well understood 122 however, the problem of heteroaromatic electrophilic substitution is still being clarified and has led to renewed interest in acid-catalyzed exchange in heterocyclic compounds.122... 

Phosphorus can be partially replaced in cyclophosp-hazene rings by some heteroelements, for example, boron, silicon, arsenic, antimony, sulftir and the broad variety of such heterocycles cannot be discussed here in any detail, but their chemistry is well covered in several reviews. Examples include boracyclophosphazenes, numerous metal-containing heterocyclophosphazenes, and sulfur-containing heterocyclophosphazenes, to name only a few (Scheme 61). 

Lothar Weber was born in 1944 in Langenols in Schlesien. He studied at the Universitat Marburg and received his doctorate there under the direction of Professor Gunter Schmid in 1973. Thereafter he carried out postdoctoral studies with Professor Barry M. Trost at the University of Wisconsin in Madison, USA. On his return to Marburg, he began the experimental work leading to his habilitation, which was completed in 1982 at the Universitat Essen. His work focused on the coordination chemistry of sulfur ylides. In 1985, he became a C2 Professor and then joined the Fakultat fiir Chemie der Universitat Bielefeld. His research interests include the chemistry of compounds with low-coordinate elements of the fifth main group, the synthesis of homo- and heterocycles with heavy elements, as well as new aspects in boron chemistry. 

Gates DP (1997) The synthesis, structure, reactivity and polymerization behavior of boron- and sulfur-nitrogen-phosphorus heterocycles and highly strained chalcogen- and boron-bridged [1], ferrocenophanes. PhD thesis, University of Toronto... 

H-1,3,5-Oxathiazines. These new heterocycles have been prepared by the reaction of aliphatic aldehydes with thioamides in acetic acid containing 100% sulfuric acid. In one case boron trifluoride etherate in chloroform was used. ... 

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