78
Tanemura and Suzuki
deprotection of 1b. Similarly, DTRT(H) lost 76% of its activity after the fifth re-cycling
for the deprotection of TBDMS ether 1d in MeOH.
In conclusion, DTRT(H) is an efficient catalyst for the tetrahydropyranylation of
alcohols and the deprotection of THP and TBDMS ethers. In addition, DTRT(H) cata-
lyzed the esterification of carboxylic acids with an equimolar amount of alcohols and the
transesterification of carboxylic esters with 1.5 equiv. of alcohols. It is important to note
that the dehydration of secondary alcohols to alkenes was largely suppressed in the syn-
thesis of esters and that the corrosion of metallic vessels is minimized. The work-up pro-
cedure is remarkably simple, and DTRT(H) is easy to handle and quite stable in air for
more than three years at room temperature.
Experimental Section
Melting points were determined on a Yamato melting point apparatus MP-21 and are
1
uncorrected. IR spectra were recorded using a JEOL FT/IR-620 spectrophotometer. H
NMR spectra were measured on a Hitachi R-1200 spectrometer using tetramethylsilane
as an internal standard. Grinding was carried out using an Absolute Mill ABS-W instru-
ment (Osaka Chemical Co.). Column chromatography was performed on Wakogel C-
200. PolyPPTS (2% cross-linked with divinylbenzene), PolyPCL (2% cross-linked with
divinylbenzene), and Montmorillonite K10 (220–270 m2/g) were purchased from
Aldrich. Mordenite (synthetic zeolite HS-690, hydrogen mordenite, 420 m2/g) was pur-
chased from Wako Chemicals. Acid densities of the resin salts were calculated from ele-
mental analyses (acid density D number of sulfur in nominal sample composition/
nominal molecular weight £ 1000). Silyl ethers were prepared using a reported method.13
THP ethers4,14 silyl ethers15, and esters10,16 were identified by comparison of their spec-
troscopic characteristics with those of authentic samples.
Synthesis of DTRT
Terephthalaldehyde (6.7 g, 50 mmol) was added to a solution of diphenylamine (16.9 g,
100 mmol) and TsOH.H2O (19.0 g, 100 mmol) in MeOH (120 mL) in a 300 mL round
bottom flask fitted with a reflux condenser with stirring using a spin bar. The solution was
stirred at room temperature for 3 h and then at 60ꢀC for 8 h. The dark green solid formed
was collected, washed with MeOH (100 mL £ 2), dried under reduced pressure (20
mmHg) for 1 h, and then ground to a powder (using a mill17 at 15,000 rpm for 1 min).
The resulting fine powder was suspended in MeOH (300 mL) and stirred for 0.5 h. The
green solid was collected, washed with MeOH (100 mL £ 3) and re-suspended and
stirred in distilled water (300 mL) and then in acetone (300 mL), washed with ether
(100 mL £ 2) and finally dried under reduced pressure (1 mmHg) to give 27.7 g (71%)
of a dark green powder, mp. > 280ꢀC, whose nominal composition was approximately
C
83.33H69.75N4.83O8.75S1.00. IR (KBr): 3398, 3020, 2969, 2921, 2854, 1699, 1599, 1556,
.
1508, 1306, 1242, 1218, 1167, 1113, 1031, 1009, 806, 788, 747, 681, 566 cm¡1
Synthesis of DTRT(H)
A suspension of DTRT (5.0 g, 14.6 mmol free amine) and TsOH¢H2O (7.5 g, 39.5 mmol)
in MeCN (50 mL) was stirred using a spin bar at 80ꢀC for 8 h in a 100 mL round bottom
flask fitted with a reflux condenser. The insoluble black powder was collected, washed
with MeCN (100 mL £ 3) and distilled water until the wash water reached a pH of 7.