With boron tribromide

Fenoldopam (76) is an antihypertensive renal vasodilator apparently operating through the dopamine system. It is conceptually similar to trepipam. Fenoldopam is superior to dopamine itself because of its oral activity and selectivity for dopamine D-1 receptors (D-2 receptors are as.sociated with emesis). It is synthesized by reduction of 3,4-dimethoxyphenylacetonitrile (70) to dimethoxyphenethylamine (71). Attack of diis last on 4-methoxystyrene oxide (72) leads to the product of attack on the epoxide on the less hindered side (73). Ring closure with strong acid leads to substituted benzazepine 74. O-Dealkylation is accomplished with boron tribromide and the catechol moiety is oxidized to the ortho-quinone 75. Treatment with 9NHC1 results in conjugate (1,6) chloride addition and the formation of fenoldopam (76) [20,21]. 

Pyrrolobenzotriazine 43 was obtained by reaction of 42 with nitrous acid. Its demethylation with boron tribromide gave 44, whose oxidation... 

The phenyl ether linkage of butoxy substituted 44 was cleaved with boron tribromide to give a hexaphenol derivative (45) in 60% yield (Scheme 14). The hexaphenol derivative was found to be remarkably soluble in most polar organic solvents, such as ethanol, DMF, DMSO, and dioxane, as well as in aqueous base solution. Condensation with octanoic acid in the presence of DCC and catalytic H+ afforded the inverse ester (46) in high yield. 

Boron tribromide cleaved a methoxyl group (e.g., 79 - 80) (Scheme 19) (65) as well as a methylenedioxy group (66). Tetrahydroberberine (26) was converted to tetrahydrocoptisine (82) by treatment with boron tribromide and subsequent methylenation (67). 

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>. 

Treating the oxide, trichloride, or metal with boron tribromide or boron triiodide has produced tribromides and triiodides for lanthanum (119). Presumably, treating the metal or the oxide with boron trichloride will produce the trichloride. 

It should be noted that one of these diols, the hydroquinone, did not provide any oligomer in the first step. This was due to the formation of the quinone structure which made it impossible to use hydroquinone directly in the substitution reaction. An alternate method was used to overcome this problem which involved the use of 4-methoxyphenol to obtain the sulfone product, followed by cleavage of the methyl ether to the diol (VIII) with boron tribromide. This set of reactions is outlined in Figure 5. 

Re NB(C6F5)3 Cl4(H20)] anion (54) is obtained as its [Bu4N]" salt in good yields,the trimeric compound [(H20)Br4ReNReBr4ReBr4N(H20)] (55) is the product of the reaction with boron tribromide. Both compounds are paramagnetic and have been characterized by EPR spectroscopy. The spectral parameters indicate a decrease of the coupling constants... 

Bromination of CF3SSCI with boron tribromide proceeds considerably better ... 

Oxidation of 48 using manganese dioxide in methanol in the presence of potassium cyanide provides clausine H (clauszoline-C) (50) quantitatively, which on ester cleavage affords clausine K (clauszoline-J) (51). Cleavage of both methyl ethers of 51 on treatment with boron tribromide led to clausine O (72) (588). 

Reaction of the iron complex salt 602 with the arylamine 921 in the presence of air led directly to the tricarbonyl(ri -4b,8a-dihydro-9H-carbazole)iron complex (923) by a one-pot C-C and C-N bond formation. Demetalation of complex 923 and subsequent aromatization by catalytic dehydrogenation afforded 3,4-dimethoxy-l-heptyl-2-methylcarbazole (924), a protected carbazoquinocin C. Finally, ether cleavage of 924 with boron tribromide followed by oxidation in air provided carbazoquinocin C (274) (640) (Scheme 5.120). 

Chemoselective demethylation of 1247 by treatment with boron tribromide led to a 4-hydroxy compound, which, after reduction with diborane, was reacted with triflic anhydride (Tf20) to afford the benzyl derivative 1248. Palladium(0)-catalyzed... 

A flask was charged with the step 2 product, the step 3 product, and /V-(3-dimcthyl-aminopropyl)-A -ethylcarbodiimide hydrochloride and then treated with boron tribromide dissolved in CH2CI2 to remove the phenol protecting group. 

Oxindole 89 was cleanly demethylated upon treatment with boron tribromide. The resulting oxindole 90 was subjected to the prenylation conditions, and the desired alkylated product 91 was obtained in 52% yield. The epoxidation/Lewis acid-mediated cyclization proved to be successful on this substrate. The epoxide product was directly treated with SnCl4 in THF to provided the desired 92. When oxindole 92 was treated with NaBHt (1.6 equivjand BF3 OEt2 (3.5 equiv) in THF, the desired 93 was obtained. The indole 93 was treated with TBDMSC1 and imidazole in DMF, to provide the required O-silylated indole, which was easily converted to the gramine 94 through the well known Mannich procedure. 

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