What does bf3 do in organic chemistry

It is one of the strongest Lewis acids an electron-pair acceptor reacting readily with chemicals containing oxygen, nitrogen, sulfur and other electron pair donors. Boron Trifluoride is used as a catalyst for organic synthesis reactions, for the manufacture of synthetic oils and lubricant additives and in the production of high-purity boron isotopes.

Boron Trifluoride BF3 can be found in a number of applications. It is used as a source for the manufacture of high-purity boron isotopes such as those found in nuclear waste containment and neutron radiation control applications as well as applications in the semiconductor industry such as the manufacture of semiconductor grade silicone. The synthesis is attractive due to its brevity in steps.

The conditions used for the rearrangement of the epoxide 22 are critical because it has the tendency to undergo further rearrangement to the ketone Boron trifluoride etherate was also used for the cleavage of epoxide during the synthesis 15 of karahana ether, a volatile monoterpene which was isolated 16 from Japanese hops.

The synthetic route is described in Scheme 7. The epoxide 27, obtained from the diene 26, on being treated with boron trifluoride etherate underwent cyclization yielding the product The cyclization probably occurred through the intermediate 27 i. Metal hydride reduction afforded diol which on tosylation yielded karahanaether The yield is unspecified. The cleavage of epoxides have been utilized for the synthesis of many terpenes like rosenolactone, 17 cyperolone, 18 maritimol.

Esterification is a frequently used reaction for the synthesis of many organic compounds. Boron trifluoride etherate —alcohol is a very convenient reagent for the esterification of many p-amino benzoic acids, aromatic, heterocyclic and unsaturated acids.

Some examples are given in Scheme 8. The acids were converted to the esters respectively in high yield on treatment with boron trifluoride etherate-alcohol reagent. Marshall and collaborators 21 used the same reagent for the esterification of carboxylic acids. Dymicky 22 prepared several formats in high yield from formic acid and alcohol in the presence of a catalytic amount of boron trifluoride -methanol complex.

The other catalysts e. Et 2 O; iii EtOH. Jackson and collaborators 23 have developed an efficient method for the conversion of alcohols and acids directly to the corresponding t-butyl derivatives in good yield using t-butyl trichloroacetimidate 36 in the presence of a catalytic amount of boron trifluoride etherate as exhibited in Scheme 9.

This method functions better with the acid sensitive groups than the traditional methods using isobutene. Less hindered hydroxyl group of a diol can be protected and also is amenable to small scale work avoiding the handing of gaseous isobutene. The t-butyl 2,2,2-trichloroacetimidate 36 is readily prepared by the addition of t-butanol to trichloroacetonitrile. Most of the experiments were carried out in presence of a mixture of dichloromethane and cyclohexane.

Acetic anhydride in presence of boron trifluoride etherate has been utilized for the of acetylation of hydroxyl group. Figure 9 Conversion of alcohols and acids from t-butyl derivatives. Reagents: 36, i BF 3. The boron trifluoride etherate has played an important role in cyclization of many, carboxylic acids, allenes etc. The following few examples will illustrate the role of boron trifluoride etherate as cyclizing agent.

The acid chloride 49 and alkene 50 were condensed to yield divinyl ketone 25 51 which underwent Nazarov cyclization 26 , 27 furnishing cyclic ketone 52 which was converted to the sesquiterpene trichodiene 53 Scheme Several allenyl aryl ketones undergo cyclization with boron trifluoride etherate affording methylene benzocyclopentenone via a new 5-endo-mode cyclization.

Probably the transformation occurred as shown in the cyclization of allenyl aryl ketone 54 into It can be observed that the presence of substituent groups in aromatic ring determines the yield of the cyclized product. Kos and Loewenthal 28 reported the cyclization of the acid 60 with boron trifluoride etherate to the ketone 61 which was converted gibberone 62 Scheme 12 in three steps:.

Figure 12 Synthesis to gibberone Reagents: i BF 3. In addition of the above mentioned reactions the following reactions also have been performed but not frequently employing boron trifluoride etherate.

Thioketalization and ketalization reaction are very important reactions for organic synthesis. Some examples are given below. The acid 63 Scheme 13 on esterification and thioketalization respectively afforded the compound 64 which on metal hydride reduction and acetylation respectively yielded the acetate The conversion of the acetate into the alcohol 66 was accomplished in three steps:.

The synthetic route is described in Scheme The ketone 69, prepared, from the ketone 68, was subjected to thioketalization to obtain the compound Desulphurization followed by catalytic hydrogenation yielded 71 whose conversion to royleanone 72 was accomplished in three steps:.

Like thioketalization, boron trifluoride etherate has been used as catalyst for the reaction of ketones with oxirane to yield ketals. The use of epoxides for ketal formation offers the advantage of being extremely gentle, operating at room temperature and under protic conditions.

Diethylene ortho carbonate converts ketones and aldehydes into their corresponding acetals in good yields at room temperature using slightly wet boron trifluoride etherate.

Figure 15 Synthesis of ketals from ketones i. Many organic compounds undergone transformation in presence of boron trifluoride etherate.

The following examples illustrate the rearrangements originated by boron trifluoride etherate. The resulting tetrahydronaphthol 38 81 Scheme 16 was methylated to yield the compound 82 and finally converted to the already reported 39 tetralone 83 Scheme Similarly, the Fries rearrangement with boron trifloride etherate was applied 40 to the acetate, prepared from the naphthol The compound 85 was treated with cerium ammonium nitrate CAN to obtain the quinone The quinone was utilized for the synthesis of eleutherins 40 87 and isoeleutherin 88 Scheme Matsumoto and collaborators 41 reported a novel rearrangement of hydrophenanthhrene into hydroanthracene with boron trifluoride etherate.

Thus the alcohol obtained by the metal hydride reduction of the enone 89 on treatment with boron trifluoride etherate suffered an interesting rearrangement yielding anthracene This method for the synthesis of anthracene was applied to the synthesis of biologically active linear abietane diterpenes.

Deslongchamps 42 reported a very interesting rearrangement of diketone 91 to 8-acetoxytwistanone 92 on treatment with a mixture of acetic acid, acetic anhydride and boron trifluoride at room temperature. The compound 92 is the first twistane derivative having a functional group at a bridge position Scheme OEt 2.

Srikrishna and collaborators 43 reported one-step method for the conversion aryl ketones into the corresponding hydrocarbons by stirring with sodium cyanoborohydride in presence of two to three equivalents of boron trifluoride etherate.

Thus the ketones were converted into the corresponding hydrocarbons respectively in high yield. These reactions were conducted at room temperature. High temperature was also used for the deoxygenation of some aryl ketones e. A mixture of boron trifluoride etherate and acetic anhydride at 0 o or below has been found to cleave different types of steroidal methyl ethers. The completely saturated ethers give the acetate with retention of configuration as the main substituent product, but the epimeric acetate and elimination products are also obtained.

A very interesting result was obtained when the demethylation experiment was tried with 4,8-dimethoxytetralone 45 with boron trifluoride etherate and acetic anhydride. The tetralone underwent aromatization yielding the acetate not the expected acetate Scheme On similar treatment the tetralone afforded the acetate These observations did not agree with the reported observation of Narayanan and Iyer on steroidal ethers.

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