Triarylcarbenium Salts Highly Reducible by Primary Alcohols

Abstract

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.

Synthesis of a Triazatriangulenium Salt

“…2-Methyl-2-butene (7.8 mL, 74 mmol) was added to the reaction mixture at À 55 8C until the yellow color faded. [9] The presence of four diastereomers was revealed by NMR spectroscopy. The product was purified by flash column chromatography (SiO 2 , hexane) to yield a 3:1 mixture of 1 and 9 (0.93 g, 2.3 mmol, 33 %) and the recovered 8 (0.79 g, 2.8 mmol, 40 %).…”

Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

“…It should also be mentioned that aromatic nucleophilic substitution of alkoxy groups in ortho-or para-positions of tritylium ions by amines, alcohols, hydroxide ions or malononitrile anions cannot be treated by eq. (1) [30][31][32][33]. However, the E values of the tritylium ions were found to be useful for determining the N and s N values of further 20 n-nucleophiles (primary amines, hydrazines, methanol, alkoxide and thiolate anions, CN -), for which kinetic data had previously been reported by Ritchie [27][28][29].…”

The Synthesis of Novel p‐Quinone Methides: O‐Dealkylation of5‐(p‐Alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ols and Related Compounds

“…sulfuric acid, obtained considerably higher yields of these useful dienones under much milder reaction conditions. [28] However, the synthesis of tricyclic p-QMs from ring systems containing seven-membered central B-rings under the above reaction conditions, has not as yet been reported.…”