Boron demethylation with

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

As an intermediate of their synthesis of [2.2]metaparacyclophane-quinones, Tashiro et al. obtained 70, that could not be completely demethylated with boron tribromide [37], Using the tert-butyl group as a positional protecting group, these authors also tried the synthesis of [2.2]metacyclophanes 72a/b containing in-traannular halide-substituents [38], The preparation of the difluoro compound... 

Quinazolinones 1 bearing a methoxy substituent in the benzene ring, readily obtained by cyclization of the appropriate precursors (cf. Section 6.3.1.1.1.), are transformed into the corresponding hydroxyquinazolinones 2 on treatment with hydrobromic acid, - hydriodic acid, aluminum trichloride,or boron tribromide. Similarly, quinazoline-2,4-diamines bearing a methoxy group at position 6 or 8 are demethylated with boron tribro-mide in dichloromethane, sodium methanethiolate in dimethylacetamide or by pyridini-um hydrochloride fusion at 200... 

The highly brominated diphenyl ether 54, isolated from the marine organism P. flava laysanica, was synthesized starting from 2,3,5-tribromo-4-methoxyphenol (55). Substrate 55 was electrolyzed at +610 mV V5. SCE (1 FmoF ) in 1 1 MeOH-CHCF containing AcOH-AcONITj and then submitted to zinc reduction leading to two dimers 56 and 57 in 26 and 43% yields, respectively. The former was demethylated with boron tribromide to give rise to the natural 54. 

The incorporation of two aryl bridgeheads, both linked in turn through the 2,6-substitution of a pyridine nucleus has provided an intermediate which has been converted to a crown ether. Thus, 2,6-bis(2, 6 -dimethoxyphenyl)pyridine after demethylation with boron tribromide or hydrogen bromide in 65% yield was reacted in dimethylsulphoxide containing potassium carbonate with the a,o)-diiodo derivative of triethylene glycol to afford a crown ether system in 22% yield (ref. 199). 

A related sequence (b) with 3,5-dimethoxyfluorobenzene gave an approach to orsellinic acids as their dimethyl ethers (ref. 112). Demethylation with boron trichloride afforded a monomethyl product, resulting from complexation of the methoxyl group adjacent to the carboxyl group, while the use of aluminium chloride in chlorobenzene gave the orsellinic acid. 

Reaction of the ArC,o unit with 1-pentynylmagnesium bromide occurred smoothly in tetrahyrofuran containing cuprous chloride without formation of alienic impurities. An analogous type of route was used for the synthesis of 1,3-dimethoxy-5-[(ZZ)-pentadec-8,11-dienyl]benzene, (15 2)-cardol dimethyl ether (ref. 105). For the synthesis of (15 2)-urushiol, 1,2-dihydroxy-3-[(ZZ)-penta-dec-8.11-dienyl]benzene and its dimethyl ether, 7-(2,3-dimethoxyphenyl)heptyl bromide and the corresponding 2,3-dihydroxy compound, obtained by demethylation with boron tribromide, have been used (ref. 149). 

The above mentioned transformation was also achieved by heating the ester (195) with quinoline and acetic acid. The resulting acidic product was subjected without purification to demethylation with boron tribromide in dichloromethane to give pisiferic acid in moderate yield. The reason for not obtaining the pisiferic acid in satisfactory yield is probably due to the decarboxylation that occurred during heating with quinoline. 

Chlorosulfonyl benzoates were synthesized from 2-aryldimethyloxazolines 17 (Scheme 5). Sequential treatment with n-butyllithium and dipropyl disulfide afforded sulfides 18. The oxazolines 18 were then hydrolyzed to the benzoic acids 19 under acidic conditions. Fisher esterification gave the esters 20, which were oxidized to the corresponding sulfonyl chlorides 21 using chlorine and aqueous acetic acid. When methoxy-substituted benzoic acids (19, X = OMe) were employed, further manipulations were performed prior to oxidation. For example, phenol (22) was prepared by demethylation with boron tribromide, subjected to esterification, and then alkylated by a variety of electrophiles to provide 23. As before, 23 was oxidized using chlorine and aqueous acetic acid. 

The final steps involved demethylation with boron tribromide, then a sequence of oxidation and reduction steps taken directly from the Nicolaou racemic synthesis (635), dehvering the unnatural isomer of diversonol (ent-932), with a superimpos-able CD spectrum to that supphed by Krohn and coworkers of the natural product (647). Hence, natural diversonol (932) is the enantiomer of the product ent-932 shown in Scheme 13.17, namely, that of (5S, 5a5,85,8af ) configuration. Also in this study, the chromone lactones lachnone C (969) and cp/-lachnone C (not shown) were synthesized enantioselectively for the first time, utihzing common synthesis intermediates (Fig. 13.14). 

Aryl methyl ethers may be demethylated with boron tribromide as shown below ... 

Ethers can be cleaved rapidly at room temperature by diborane and halogen 0-Demethylation with retention of O-tosyl groups can be achieved with boron trichloride Alcohols can be obtained by degradation of carboxylic acids through carboxy-inversion of acyl peroxides . Aldehydes can be efficiently decarbonylated under mild conditions in the presence of a rhodium complex . A new mild and potentially selective method for the prepn. of aliphatic... 

This compound is synthesized from 3,4-OMe-TTP by demethylating with boron tribromide. 

The first involved cyclisation of 3, 5 -dimethoxy-3-bromopropion-anilide to the carbostyril (XVII), which was condensed with 2-iodobenzoic acid and the product cyclised to (XVIIIa). The methyl ester (XVIIIb) was demethylated with boron trichloride to (XVIIIc), which gave (XVIIId) on... 

Preparation from 5-ethyl-2,4-dimethoxyacetophenone by demethylation with boron tribromide in methylene chloride at r.t. (36%) [2678,2679]. 

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