1.1.1- Trifluorides amines carboxylic acids

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

Hydrolysis of the ethyl ester proceeded smoothly using hydrochloric acid in acetic acid to give carboxylic acid 69 in 88% yield (Scheme 4.9). Previously, amines were allowed to react with the carboxylic acid core in hot DMSO to deliver the C7 products however, the difluoroborate 70, derived from the carboxylic acid 69, greatly increased the reactivity of the C7 position. Consequently, the displacement of the C7-F with amines was accomplished at lower temperature (Baker et al., 2004 Cecchetti et al., 1996 Domalaga et al., 1993 Ellsworth et al., 2005a,b Hu et al., 2003). In this event, the carboxylic acid was allowed to react with boron trifluoride to deliver difluroboronate 70 in excellent yield. The thus afforded borate ester reacted with A -methylpiperidine in DMSO in the presence of triethylamine at ambient temperature to furnish ( —)-ofloxacin (1, levofloxacin) in 56% yield. 

O-tert-Butyl trichloroacetimidate, prepared in 70% yield by reacting potassium rerr-butoxide with trichloroacetonitrile, reacts with carboxylic acids and alcohols in the presence of a catalytic amount of boron trifluoride etherate at room temperature in cyclohexane-dichloromethane [Scheme 6.35], 7 The method also converts alcohols to ferr-butyl ethers (see section 4.3.2). A very similar reaction that allows /erf-butylation under essentially neutral conditions on a large scale involves reaction of a carboxylic acid with 3-4 equivalents of JV,N -di-isopropyl-Orerf-butylisourea88 [Scheme 6,36].56S9 The reaction proceeds via a tertiary carbocation ion intermediate and since capture of the cation is inefficient, excess isourea is required. The presence of alcohols is tolerated but not thiols or unhindered amines. The reaction conditions are compatible with a range of acid sensitive groups such as AMrityl derivatives and cydopentylidene acetals.90... 

Naturally, it is possible to synthesise a similar ligand system without central chirality and in fact without the unnecessary methylene linker unit. A suitable synthesis starts with planar chiral ferrocenyl aldehyde acetal (see Figure 5.30). Hydrolysis and oxidation of the acetal yields the corresponding carboxylic acid that is transformed into the azide and subsequently turned into the respective primary amine functionalised planar chiral ferrocene. A rather complex reaction sequence involving 5-triazine, bromoacetal-dehyde diethylacetal and boron trifluoride etherate eventually yields the desired doubly ferrocenyl substituted imidazolium salt that can be deprotonated with the usual potassium tert-butylate to the free carbene. The ligand was used to form a variety of palladium(II) carbene complexes with pyridine or a phosphane as coligand. 

Amidation of carboxylic acids. Boron trifluoride etherate has been used as a reagent for reaction of carboxylic acids with primary or secondary amines to form amides. The reaction is accelerated by bases (triethylamine, DBU) and by azeotropic removal of the water formed. The reaction is conducted in refluxing benzene or toluene. Yields are generally in the range of 50-85%. 

Only one example was found where this class of amino acids was produced. Oxidation of 7.246 gave a ketone and treatment with boron trifluoride led to the conjugated ketone, 7.247.132 Conjugate addition of azide, reduction to the amine and cyclization gave diastereomeric methyl 9-(3-hexyl-2-aziridino)nonanoic acid (J.248 and 7.249). The final step in that sequence proceeded in only 37% yield. If the alkenyl moiety was converted to an epoxide moiety, aziridine carboxylic acids were prepared in good yield, via the azide.132... 

Lewis acids like tetrachlorosilane in pyridine or titanium tetrachloride are reported to give simple amides in moderate yields. Boron trifluoride etherate in the presence of a strong base amidates carboxylic acids in an excess of primary amine. These reactions have not found broad application. 

Deshmukh et al. demonstrated that triphosgene can also be used to prepare dialkylcar-bamoyl azides from tertiary amines and sodium azide. Alternatively, acyl azides (e.g. 303) can be converted via a one-step procedure from carboxylic acids using bis(2-methoxyethyl)aminosulfur trifluoride (Deoxo-Fluor) (Scheme 3.46). ... 

Acylation of 3-substituted indoles is more difficult, however 2-acetylation can be effected with the aid of boron trifluoride catalysis." " Indoles, with a carboxyl-containing side-chain acid at C-3, undergo intramolecular acylation forming cyclic 2-acylindoles." Intramolecular Vilsmeier processes, using tryptamine amides, have been used extensively for the synthesis of 3,4-dihydro-p-carbolines, a sub-structure found in many indole alkaloids (P-carboline is the widely used, trivial name for pyrido[3,4-fc]indole). Note that it is the imine, rather than a ketone, that is the final product the cyclic nature of the imine favours its retention rather than hydrolysis to amine plus ketone as in the standard Vilsmeier sequence " this ring closure is analogous to the Bischler-Napieralski synthesis of 3,4-dihydro-isoquinolines (9.15.1.7). 

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