Boron Trifluoride Etherate hydrolysis

The successful labeling of the elusive 14a-position in cholestane represents a very important application of this reaction.It is known that hydroboration of the double bond in 5of-cholest-14-ene (174) occurs on the a-side. Consequently, by using deuteriodiborane (generated by the reaction of boron trifluoride etherate with lithium aluminum deuteride) and then propionic acid for hydrolysis of the alkylborane intermediate, 14a-d,-5a-cholestane (175) is obtained in 90% isotopic purity. This method also provides a facile route to the C-15 labeled analog (176) when the alkylborane derived from 5a-cholest-14-ene is hydrolyzed with propionic acid-OD. ... 

Tetrahydrofuran itself can be opened using either the stoichiometric or the catalytic version of arene-promoted lithiation, but both cases need the activation by boron trifluoride. The catalytic reaction was performed by treating the solvent THF 324 with the complex boron trifluoride-etherate and a catalytic amount (4%) of naphthalene. The intermediate 325 was formed. Further reaction with carbonyl compounds and flnal hydrolysis yielded the expected 1,5-diols 326 (Scheme 95), which could be easily cyclized to the corresponding substituted tetrahydropyrans under acidic conditions (concentrated FlCl). 

Benzoxathiolium salts have proven to be effective masked acylating agents (79S223). 2-Substituted 1,3-benzoxathiolium tetrafluoroborates have now been utilized in the preparation of esters. Reaction of the salt (334) with two equivalents of an alcohol gave the 2-alkoxy-2-alkyl-benzoxathiole (335). Hydrolysis of (335) with red mercury(II) oxide and boron trifluoride etherate in aqueous THF delivered ethyl benzoate in excellent yield (Scheme 72). 

The orf/to-formylation of 2-aminopyridines can be effected via the rearrangement of the azasulfonium salt prepared from a 2-aminopyridine, 1,3-dithiane, f-butyl hypochlorite and sodium methoxide (74CC685). The crude sulfilimine (815) was refluxed in f-butanol containing potassium f-butoxide to yield the dithioacetal (816). Hydrolysis of (816) with mercury(II) oxide/boron trifluoride etherate gave the aldehyde (817 Scheme 191). This method should be applicable to the formylation of other heterocyclic amines. 

We also found that ester functionality was compatible with this reduction sequence. Thus, treatment of the ester-lactone 81 with sodium borohydride and boron trifluoride etherate provided the tetrahydropyran 123 in 55% purified yield. Upon reaction with sodium hydroxide, 81 underwent simple ester hydrolysis to furnish the carboxylic acid 127 (see Table 3). 

The tiyptophol was condensed with methyl propionylacetate using boron trifluoride etherate as the catalyst to produce tetrahyropyranoindole. Basic hydrolysis of the ester gave [3-14C] etodolic acid (overall yield 26% from the labeled starting material). The compound was recrystallized in presence of an antioxidant to prevent formation of peroxides and stored at -10°C. The radiochemical purity was determined to be 99%. 

Stereochemically well-defined silylaminoalcohols can also be prepared through the hydrolysis of intermediate oxazolines obtained by treating chiral a-silylepoxides with acetonitrile in the presence of boron trifluoride etherate.312... 

Reports) was converted (by a modified Curtius reaction) into the corresponding isocyanate, which was cyclized in 70—90% yield into the lactam (26), using boron trifluoride etherate. Since these represent new conditions for effecting such a reaction, generalization to a number of substituted phenethyl isocyanates was carried out. Compound (26), upon successive acetoxybromination, dehydro-bromination, and hydrolysis, gave the target compound (27), whose quasi-axial a-OH configuration was deduced from n.m.r. data. 

The tetrazole analogue (341) of 7-oxocholest-5-en-3/3-yl acetate has been prepared 82 by reaction of the afi-unsaturated ketone with hydrazoic acid and boron trifluoride etherate hydrolysis of the 3)3-acetate and oxidation of the resultant alcohol furnished 7a-aza-B-homocholest-4-eno[7a,7-d]tetrazol-3-one. Cycloaddition of ethylenediamine to 2a-bromo-5a-cholestan-3-one has furnished a simple one-step route to 5 -cholestane[2,3-e]dihydro-2,3-pyrazine (342).183 Analogous cycloaddition has been achieved using 16a-bromoandrostan-17-ones. 

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. 

For example, condensation of silyl enol ether (3.21) of 3-pentanone with 2-methylbutanal in the presence of TiC gives the Ti-complex 3.22, which on hydrolysis yields an aldol product, manicone (4,6-dimethyl-4-octen-3-one) (3.23), an alarm pheromone. Treatment of 3-pentanone with LDA results in the formation of an enolate, which is trapped with chlorotrimethylsilane to give 3.21. Other Lewis acids such as tin tetrachloride (SnCU) and boron trifluoride etherate (BF3-OEt2) can also be used. 

Explain the following observations (a) hydrolysis of epoxy-cyclopentene (5) with dilute acid gave a mixture of 1,2-dihydroxy-cyclopent-3-ene (20%) and 1.4-dihydroxycyclopem-2-ene (80%) (b) treatment of the epoxide of 1,2-diphenylethene (stilbene) with boron trifluoride etherate gave an isomeric compound which formed a 2,4-dinitrophenylhydrazone and was oxidized to an acid, Ci Hi O,. 

By the Darzens reaction. -ionone afforded a C14 aldehyde which as the diethyl acetal underwent addition to ethyl vinyl ether in the presence of boron trifluoride etherate to yield a Cl6 acetal. After hydrolysis, loss of ethanol and formation of the diethyl acetal as before, reaction under acidic condiions with ethyl propenyl ether gave the unsaturated Cl9 aldehyde after hydrolysis and removal of ethanol. Reaction of two moles with ethyne dimagnesiuro bromide produced the C40 chain and dehydration of the diol, selective catalytic hydrogenation followed by isomerisation completed a remarkable technical synthesis of i-carotene. Further variations have involved the use of two moles of the C14 aldehyde and a Cl2 divinyl ether. An independent approach (ref.29) has utilised vitamin A (32) converted to a phosphonium salt, thence to the corresponding phosphoran, autoxidation of which afforded s-carotene ( scheme 16). 

The first total synthesis of ( )-lycoridine margetine (33), a member of the non-basic alkaloids which possess antimitotic activity has been achieved (Scheme 3). The homoallylic alcohol (26) served as a latent diene in a Diels-Alder reaction with ethyl acrylate to give a diastereomeric mixture of adducts which upon base equilibration and hydrolysis provided the tmns-acid (27). Modified Curtius reaction on (27) afforded the corresponding isocyanate which was cyclized to the lactam (28) in 89% yield by a new method using boron trifluoride etherate. Compound (28) was converted into an N-acetyl derivative which upon basic hydrolysis gave the acid (29). Treatment of (29) with NBS followed by reflux in pyridine solution gave the lactone... 

The second approach to (50) was more direct. Acetylation of (51) was followed by sequential treatment with oxalyl chloride and excess diazomethane to afford, after hydrolysis, the diazoketone (53). Boron trifluoride etherate in nitromethane proved to be the best system to catalyse the cyclization of (53) to (50). This route may provide a useful intermediate for syntheses of atisine-type alkaloids. 

Following a route previously developed for the synthesis of deacetamidocolchicine, (+)-colchicine has been synthesised from (136 R = R = OMe), which was hydrolysed by acid to (136 RR = 0) and this was cyclised by boron trifluoride etherate to the acid (137). Ring-expansion of the methyl ester of (137) with trifluoroacetic acid gave a mixture of (138) and the isomeric ag-unsaturated ester, both of which, on oxidation, gave the tropolone (139), hydrolysis and decarboxylation of which gave deacetairaido-isocolchicine. Hydrolysis of (139) and treatment with diphenyl-... 

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