2,4,6-Trimethoxyphenyllithium, Φ′Li[Φ′ = 2,4,6-(MeO)3C6H2], reacted with diphenyl carbonate and with ethyl formate to give tris(2,4,6-trimethoxyphenyl)methanol, Φ′3COH (1), and bis(2,4,6-trimethoxyphenyl)methanol, Φ′2CHOH (2), respectively. Compound 1 reacted with a slight excess of perchloric acid in 2-propanol to give very dark-purple crystals of the triarylcarbenium salt, [Φ′3C]X (3, X = ClO4), which were inert even in hot ethanol. However, a treatment of 3 (X = Cl), prepared in situ in 1 M (1 M = 1 mol dm−3) hydrochloric acid, with 1 M sodium hydroxide resulted to give 4-bis(2,4,6-trimethoxyphenyl)methylene-3,5-dimethoxy-2,5-cyclohexadienone. Compound 2 also reacted with a slight excess of perchloric acid in methanol to give dark-red crystals of the diarylcarbenium salt, [Φ′2CH]X (5, X = ClO4). Compound 5 was considerably inert even in hot methanol, but was easily reduced in primary and secondary alcohols to give bis(2,4,6-trimethoxyphenyl)methane, Φ′2CH2. Measurements of the half-lives of 5 in these alcohols showed that 5 was more labile in secondary alcohols, such as 2-propanol and 2-butanol, than in primary alcohols. When a suspension of 5 (X = Cl), prepared in situ in 1 M hydrochloric acid, was heated, tris(2,4,6-trimethoxyphenyl)methane, Φ′3CH (7), was obtained. Analogous reactions to give 7 were observed in methanol containing a slight excess of hydrochloric acid or nitric acid in place of perchloric acid. The possible paths of these reactions are discussed.

A series of triarylmethanols bearing o-methoxyl groups (1a: [2,6-(MeO)2C6H3]3COH, 1b: (2-MeOC6H4)[2,6-(MeO)2C6H3]2COH, 1c: Ph[2,6-(MeO)2C6H3]2COH, 1d: [2,5-(MeO)2C6H3]3COH, 1e: Ph2[2,6-(MeO)2C6H3]COH) were prepared. Corresponding carbenium salts, [Ar3C]X 2a—c, were isolated by short-period treatments of Ar3COH 1a—c with a slight excess of acid in some bulky alcohols, such as 2-propanol or 2-methyl-1-propanol. The high basicity of 1a—c was explained by through-space interactions of a pair of 2p electrons of an o-methoxyl oxygen with an empty 2p orbital of the resulting carbenium carbon. In ethanol, 1-butanol or 3-methyl-1-butanol, 1c, as well as 2c, was reduced under very mild conditions to triarylmethane, Ar3C–H 3c, and in other bulkier alcohols it was reduced under more forcing conditions. The formations of aldehyde or ketone, the by-product, were confirmed in some cases. Compounds 1a,b,d,e, as well as 2a,b, reacted in analogous manners under more forcing conditions. The reaction rates in several alcohols increased in the order 2a < 2b < 2c, and the reaction rates of alcohol for 2c decreased in the order ethanol > 3-methyl-1-butanol > 1-butanol > 2-propanol > methanol > 2-butanol > 2-methyl-1-propanol. Compounds 2b,c were also reduced in tetrahydrofuran, and formed xanthene derivatives in dimethyl sulfoxide or in water.

In the presence of a catalytic amount of acid, the title xanthenol (1) reacted in acetone to give 1,8-dimethoxy-9-phenylxanthen-9-ylmethyl methyl ketone. Analogous reactions were observed for ethyl methyl ketone and acetophenone, but not for diethyl ketone. Propanal and butanal also reacted to give 2-(1,8-dimethoxy-9-phenylxanthen-9-yl)propanal and 2-(1,8-dimethoxy-9-phenylxanthen-9-yl)butanal, respectively. In hot primary and secondary alcohols, 1 was reduced to give 1,8-dimethoxy-9-phenylxanthene. 1 also reacted with methoxybenzenes, phenol, and N-alkylanilines to give 9-aryl-1,8-dimethoxy-9-phenylxanthenes. The basicity of 1, or the stability of the carbenium ion (pKR+ = −0.81), was measured in hydrochloric acid and compared with those of related 9-arylxanthen-9-ols, such as 1,8-dimethoxy-9-(2,6-dimethoxyphenyl)xanthen-9-ol (1.14), 9-(2,6-dimethoxyphenyl)xanthen-9-ol (4.80) (8), and 9-phenylxanthen-9-ol (0.75). The drastic differences in the reactivities and the basicity between 1 and 8 were attributed to a steric effect rather than an electronic effect.

Triarylmethanols of type (4-YC6H4)Φ2COH {Φ = 2,6-(MeO)2C6H3; Y = MeO, Cl, Me2N} were prepared. The methanol, (4-MeOC6H4)Φ2COH, reacted with acids in a variety of solvents to give the triarylcarbenium salts, [(4-MeOC6H4)Φ2C]X or [(4-HOC6H4)Φ2C]X, or 4-bis(2,6-dimethoxyphenyl)methylene-2,5-cyclohexadienone, O=C6H4=CΦ2, depending on the conditions. These carbenium salts further reacted in alcohols, ROH, to give the triarylmethanes, (4-ROC6H4)Φ2CH (R = Me, Et), where the para-substituent, MeO or HO, was substituted by the solvent, accompanied by a reduction at the central carbon. The methanol, (4-ClC6H4)Φ2COH, also reacted with acid to give the carbenium salt or the triarylmethane, depending on the conditions. While the methanol, (4-Me2NC6H4)Φ2COH, also gave the carbenium salt, [(4-Me2NC6H4)Φ2C]X, it was inert against the formation of the triarylmethane under analogous conditions. It reacted with aqueous sodium hydroxide to give O=C6H4=CΦ2 rather than the original methanol. The para-substituent of [(4-MeOC6H4)Φ2C]X was substituted by di- and monoalkylamines, RR′NH, to give [(4-RR′ NC6H4)Φ2C]X (R,R′ = Me,Me; Et,Et; Me,H; Et,H; Bu,H). While [(4-ClC6H4)Φ2C]X reacted with the dialkylamines to give [(4-RR′NC6H4)Φ2C]X, it reacted with monoalkylamines, RNH2, to give [(4-ClC6H4)Φ2C–NRH2]X. [(4-Me2NC6H4)Φ2C]X was hydrolyzed in the presence of diethylamine to give O=C6H4=CΦ2, but reacted with monoalkylamines to give RN=C6H4=CΦ2.

Unusual Stabilities and Reactivities of Tris-and Bis(2,4,6trimethoxyphenyl)carbenium Salts. --(WADA, M.; KONISHI, H.; KIRISHIMA, K.; TAKEUCHI, H.; NATSUME, S.; ERABI, T.; Bull. Chem.