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1,3,4-Thiadiazolium-3-(unsubstituted) methanides have been trapped with substituted alkyne dipolarophiles at –60 °C giving high yields of 2,3-di- and 2,3,4-tri-substituted 1-{[1-(vinylthio)-1-phenylmethylidene]amino}pyrroles from a cycloaddition rearrangement sequence. The conformation of these molecules results in an unusual proton shielding effect in the 1H NMR spectra. An X-ray crystal structure is reported for methyl 1-{(Z)-1-[(Z)-2-methoxycarbonylvinylthio]-1-phenylmethylideneamino}-2-phenyl-1H-pyrrole-3-carboxylate 7a.

Quaternisation of 3,5-diaryl-1,2,4-thiadiazoles with trimethylsilylmethyl triflate at 40 °C occurred at N-2. Separate desilylation of the salts resulted in a ring expansion to substituted 2H-1,3,5-thiadiazines 5. Heating of these with ethanolic sodium ethoxide caused sulfur extrusion and ring contraction to 2,4-disubstituted imidazoles 6. 3,4-Diaryl-1,2,5-thiadiazoles were less reactive to alkylation and trimethylsilylmethylation required heating at 80 °C. Treatment of the salts with CsF unexpectedly gave 1-trimethylsilylmethyl-4,5-diarylimidazoles 21. 1H, 13C, 15N NMR spectra are described and the mechanisms were studied by ab inito calculations with the GAUSSIAN94 series of programmes using the HF/6-31G* theoretical level.

The first examples of a bowl-shaped tricyclic nitrogen-sulfur analogue of the tri-pentagon bowl are reported; substituted 5,6,7,7a-tetrahydropyrrolo[2,1-b]-1,3,4-thiadiazole-endo-6,7-dicarboxyimides are synthesised by a relatively simple route.

A novel cascade cyclisation protocol has been developed which ‘zips up’ two rings to form new tetracycles. In the protocol, treatment of vinyl bromides and iodides with hexamethylditin (Me3Sn˙) yields intermediate vinyl radicals which undergo 5-exo cyclisation onto nitrile groups to yield intermediate iminyl radicals. The iminyl radicals can undergo 6-endo cyclisation (or 5-exo followed by neophyl rearrangement) to yield tetracyclic π-radicals which lose hydrogen (H˙) in an H-abstraction step. Methyl radicals, generated from the breakdown of trimethylstannyl radicals (Me3Sn˙), are proposed as a possible H-abstractor for this final oxidative step. The protocol has been used to synthesise the tetracyclic rings A–D (tetracycle indolizino[1,2-b]quinolin-9(11H)-one) of the anticancer alkaloids camptothecin, mappicine, nothapodytine B and nothapodytine A. The protocol has also been applied to the synthesis of analogues of camptothecin in which ring A has been replaced by thiophene (8,10-dihydrothieno[2′,3′:5,6]pyrido[2,3-a]indolizin-8-one) and ring D by pyrrole (10H-pyrrolizino[1,2-b]quinoline) and benzene (11H-indeno[1,2-b]quinolin-11-one).

Lithium borohydride absorbs anhydrous ammonia to form four stable ammoniates; Li(NH(3))(n)BH(4), mono-, di-, tri-, and tertraammoniate. This paper focuses on the monoammoniate, Li(NH(3))BH(4), which is readily formed on exposure of LiBH(4) to ammonia at room temperature and pressure. Ammonia loss from Li(NH(3))BH(4) commences around 40 degrees C and the compound transforms directly to LiBH(4). The crystal structure of Li(NH(3))BH(4) is reported here for the first time. Its close structural relationship with LiBH(4) provides a clear insight into the facile nature and mechanism of ammonia uptake and loss. These materials not only represent an excellent high weight-percent ammonia system but are also potentially important hydrogen stores.