Boron tribromide trimethyl

Conversion to a more facile, sulfur-derived, leaving group can be achieved by treatment with sodium thiosulfate or salts of thio and dithio acids (75,87). Under anhydrous conditions, boron tribromide converts the 3 -acetoxy group to a bromide whereas trimethyl silyl iodide gives good yields of the 3 -iodide (87,171,172). These 3 -halides are much more reactive, even when the carboxyl group is esterified, and can be displaced readily by cyano and by oxygen nucleophiles (127). 

Hydroxythiadiazole and neat trimethyl orthoacetate showed a 20 80 ratio of N- versus O-alkylation products by H NMR <2002EJ01763>. The acidic hydroxyl group of thiadiazole 130 can be selectively protected as the benzyl ether 113 (Equation 22) <2004TL5441>. Nonhydrogenative debenzylation of the bisbenzyl thiadiazole 116 was achieved with boron tribromide to afford the bis-l,2,5-thiadiazole 131 (Equation 23) <2004TL5441>. 

ETHERS Boron tribromide. Ceric ammonium nitrate. N-Ohlorosuecinimide, Sodium N-methylanelide-Hexamelhyl-phosphoric triamide. Thallium(III) nitrate. Trimethyl(phenylthio)silane. 

Trimethyl Telluronium Tetrabromoborate1 1.69 g (6.7 mmol) of trimethyl telluronium bromide and lSg (60 mmol) of boron tribromide are mixed in a vacuum line trap, the mixture is stirred magnetically at 20° for 8 h, and excess boron tribromide is then removed to leave the colorless product m.p. 215 (dec ). 

Obtained by treatment of its trimethyl ether with boron tribromide (6 equiv) in methylene chloride, first at -78°, then at -20° (>72%) [1658]. 

---