637. The interaction of boron trichloride with unsaturated alcohols and ethers

Abstract

Interaction of unsaturated alcohols (allyl, methallyl) (1, 2, and 3 mols., severally) with boron trichloride ( 1 mol.) gave the appropriate dichloroboronites, chloroboronates, and trialkenyl orthoborates. The alkenyloxyboron chlorides, which were also obtained from the borates and boron trichloride, were unstable, decomposing to the appropriate chloroalkene, but stable 1 : 1 and 1 : 2 complexes were obtained with pyridine. Neither these borates nor tripropynyl borate was attacked by hydrogen chloride a t 20°, but at 120' triallyl borate was dealkylated. Dealkylation by both hydrogen bromide and hydrogen iodide was accompanied by addition. Diallyl and dimethallyl ethers were easily cleaved by boron trichloride ; the mixed allyl methallyl ether reacted by methallyl-oxygen fission. Neither ammonia nor pyridine co-ordinated with triallyl borate, and the reaction with bromine was slow.STUDIES 1 on boron trichloride-alcohol and -ether systems have been extended to unsaturated compounds. The reactions of allyl and methallyl alcohols and their mixed and simple ethers and of propynol show a broad similarity to those of corresponding saturated systems, except that certain reactions are accompanied by addition. The allyl and the methallyl group appear to have reactivities intermediate between those of sec.-and tert.-alkyl groups.Triallyl borate,2 obtained in poor yield, is the only borate previously prepared by the interaction of boron trichloride and an unsaturated alcohol , although the preparation of triallyl3 and trimethallyl * borate from other starting materials has been described.Allyl, methallyl, and propynyl orthoborate have now been prepared in good yield by addition of boron trichloride (1 mol.) to the appropriate alcohol (3 mols.) in n-pentane at -80"; the reverse order of addition was less successful. By alteration of the relative proportions of the reagents evidence of the formation of intermediate alkenyloxyboron chlorides was obtained : BCI, + RO.BCI, -> (RO),BCI ,-+ B(OR),Of the alkenyloxyboron chlorides, the dichloroboronites, RO-BCl,, could not be adequately characterised owing to their instability, but stable 1 : 2 complexes with pyridine, and in the allyl system also a 1 : 1 complex, were obtained. The chloroboronates, (RO),BCl, whilst still unstable, were not as easily decomposed as the dichloroboronites ; a 1 : 2 complex with pyridine was obtained from diallyl chloroboronate, whilst the dimethallyl compound afforded a 1 : 1 complex. The alkenyloxyboron chlorides were also obtained from the appropriate orthoborate and boron trichloride ; their decomposition followed the general scheme observed earlier in saturated systems : l b 9 5 9 6General resemblance to saturated systems has been noted. BCl, BCl, B(OR), + (RO),B*CI + RO-BC1, 3RO*BC12 __t 3RC1 + B203 + BCI, 3(RO),BC1< 3RC1 + B,O, + B(OR),Pyrolysis of the 1 : 1 complex between allyl dichloroboronite and pyridine was similar to that observed with the n-butyl analogue,' whilst the 1 : 1 complex between dimethallyl

Reactions Of Boron Trichloride With Organic Compounds

“…in an inert solvent such as n-pentane. It has been demonstrated with a selection of primary [R = n-C3H7 (64); n-C4H9, f-C4H9 (61); n-C5Hu (2); ¿-C4H9CH2, n-C8H17 (64); = 2, CH2=C(CH3)CH2 (71); CH3CH=CHCH2, CH2=CHCH2CH2 (74); CH=CCH2 (71); C1(CH2)2 (46); C1(CH2)3 (2); C1(CH2)« (46); C1(CH2)5, CH2C1CHC1CH2 (2); CC13 (22); CF,CH2 (4); C2H6OOCCH2, C2H6OOC(CH2)2 (52)] and also secondary alcohols [R = s-C4H9 (61); f-C3H7(CH3)CH, ¿-C4H9(CH3)CH (64); n-C6H13(CH3)CH (60); CH2=CH(CH3)CH ( 74 Exceptions were those alcohols [R = C6H5CH2 (7), CeHs(CH3)CH (60)] which have a propensity for preionization, when the major product was the alkyl chloride (equation 3), this being the exclusive stoichiometry for an unsubstituted tertiary alcohol (R = ¿-C4H9 ( 61)). Boron trichloride may, however, be used for the preparation of tert-alkyl (as well as less highly branched) borates, by adding the trichloride (1 mole) to a mixture of the alcohol and pyridine (3 moles of each) in an inert solvent such as n-pentane, chloroform, or methylene dichloride at low temperature ( -10°to -80°C.…”

“…Under the conditions of the experiments (i.e., rapid reaction, low temperature, and high dilution) reaction 17 can only be of importance for alcohols having great tendency for preionization (e.g., R = i-C4H9, 5 2, C6H5(CH3)CH, allyl), and as water is a product of equation 17, it could initiate a chain reaction because boron trichloride is of course readily hydrolyzed to hydrochloric acid and boric acid. Trialkyl borates react (equation 18) with hydrogen chloride, but again only if the alkyl group is electron-releasing (7,60,61,71). d(+)-Tri-1 -phenylethyl borate gave much racemized but configuration-retained 1-chloro-l-phenylethane (a similar stereochemical result was obtained from ROH and BC13) (60), whereas the triallyl borate-hydrogen chloride reaction, which only proceeded at high temperature, was accompanied by anti-Markownikoff addition to give tri-3-chloropropyl borate and 1,2-dichloropropane (71).…”

“…Trialkyl borates react (equation 18) with hydrogen chloride, but again only if the alkyl group is electron-releasing (7,60,61,71). d(+)-Tri-1 -phenylethyl borate gave much racemized but configuration-retained 1-chloro-l-phenylethane (a similar stereochemical result was obtained from ROH and BC13) (60), whereas the triallyl borate-hydrogen chloride reaction, which only proceeded at high temperature, was accompanied by anti-Markownikoff addition to give tri-3-chloropropyl borate and 1,2-dichloropropane (71).…”

“…(iii) 1-Chloroalkyl methyl ethers reacted according to equation 32 (48). (iv) Mixed dialkyl (48,60,63), diallyl (71), or alkyl allyl (72) ethers gave alkyloxy(or allyloxy) boron compounds and alkyl (or allyl) chlorides [the chlorides from the more electron-releasing (R' in ROR') of the two groups], according to equations 33 or 34; chloroboronates did not react with ethers. In certain cases, depending on the stabilities (see Section III) of the particular alkoxyboron chloride (or on the addition of a trace of Lewis acid), the reactions were modified according to scheme 33a (71, 74) or 34a (63, 71, 72).…”

“…Complexes of the following ethers have been characterized: (CH3)20 ( 163), (C2H5)20 (133), CH30CH2C1 (48), CH30CH2CH2C1, C2H60CH2CH2C1, (C1CH2CH2)20, (ra-C4Hg)20. The relative ease of decomposition of the 2-chloroethyl ether complexes was ethyl > methyl > s-CiHgOC^s-i (63) n-Cs/7"OC2Hs (63) TABLE 1 Fission of RO-R' according to equations 33 and 34 n-CtHniCH^CHOC.R, (60) CH2=CHCH2OC3.K,-¿ (72) CtHi{CHt)CHOCiFi-0 (60) ClCH2CH2OCff3 (48) CH2=CHCH20CH2(CHs)C=CH2 (71) C1CH2CH20C2H5 (48) CH^CHCHiOCMs-n (72) C6HsOCH, (63) CH^CHCELCXhffg-s (72) 06 30 2-chloroethyl (48). Although n-butyl isobutyl ether formed an unstable 1:1 complex with boron trichloride at -80°C., there was no evidence that such a complex formed with ethyl 1-methylheptyl ether under similar conditions.…”