Vidar Bjørnstad

Pyrolysis of Cyclic Polyoxo Phosphorus Ylides

In an extension of our recent work on generating acetylenic amino acid derivatives by flash vacuum pyrolysis (FVP) of appropriate stabilised phosphorus ylides,1 we examined the ylides 1 with a free amino group. Rather than the expected acetylenic product these gave the novel cyclic ylides 2 with loss of ethanol. Preliminary attempts to bring about extrusion of Ph3PO from these gave rather confusing results so we have examined simpler cyclic ylides in an attempt to understand the processes involved.

Regioselective Methylenation and in situ Methanolation of Ketones Prone to C-C Double-Bond Isomerisation

An efficient methylenation reaction in isomer-labile ketones is described. The methylenation reaction is based on an improved method for the formation of bis(iodozincio)methane [CH 2 (ZnI) 2 ]. A subsequent in situ hydroboration-oxidation sequence provides the corresponding methanol derivatives in high yields without double-bond isomerisation.

Chlorinated thiophenes. Part 2. Trihalogenated hydroxythiophenes; preparation, reactions and tautomeric properties

2-Hydroxy-3,4,5-trichlorothiophene (4), 3-hydroxy-4-bromo-2,5-dichlorothiophene (5) and 3-hydroxy-2,4,5-trichlorothiophene (6) have been synthesised. It was found that 4 exists in a carbonyl form, whereas in 5 and 6 the hydroxy forms were the major tautomers. Several derivatives of the trihalogenated hydroxythiophenes were prepared. O-Methylation was carried out with diazomethane and O-acetylation with acetyl chloride. Silylation of 4 was performed using N,O-bis(trimethylsilyl)acetamide. Compound 4 reacted with methylmagnesium iodide in an unexpected way by exchanging chlorine with magnesium iodide, giving 3,4-dichloro-2,5-dihydrothiophen-2-one (16) after hydrolysis. In an unsuccessful attempt to try to prepare thiophene isosteres of the infamous 2,3,7,8-tetrachlorodibenzo-p-dioxine, the new dimer 2,2′,3,3′,4,4′-hexachloro-2,2′,5,5′-tetrahydro-2,2′-bithiophen-5-one (15) was discovered, the crystal structure of which is reported.