November 2006
1621
Table 2. Aerobic Photooxidation for Various Alcohol Substrates
In conclusion, this new method for the preparation of ben-
zaldehydes and a,b-unsaturated aldehydes is convenient in
the viewpoint of using visible light irradiated from a general-
purpose fluorescent lamp instead of UV light from a high-
pressure mercury lamp, and is thought to be environmentally
benign, due to all the factors of the use of molecular oxygen
as terminal oxidant, EtOAc of environmentally low impact as
solvent, catalytic amount of iodine and no metals. The study
of scale-up of this reaction is now in progress in our labora-
tory.
Entry
1
Substrate
Product (yield %)a)
(87)
2
3
4
5
(87)
(53)
(83)
(81)
References and Notes
1) “Comprehensive Organic Transformations: A Guide to Functional
Group Preparations,” ed. by Larock R. C., Wiley-VCH, New York,
1999.
2) Ohkubo K., Suga K., Fukuzumi S., Chem. Commun., 2006, 2018—
2020 (2006).
3) Guan B., Xing D., Cai G., Wan X., Yu N., Fang Z., Yang L., Shi Z., J.
Am. Chem. Soc., 127, 18004—18005 (2005).
4) Mu R., Liu Z., Yang Z., Liu Z., Wu L., Liu Z.-L., Adv. Synth. Catal.,
347, 1333—1336 (2005).
5) Schultz M. J., Hamilton S. S., Jensen D. R., Sigman M. S., J. Org.
Chem., 70, 3343—3352 (2005).
6
(84)
6) Liu R., Liang X., Dong C., Hu X., J. Am. Chem. Soc., 126, 4112—
4113 (2004).
7) Mori K., Hara T., Mizugaki T., Ebitani K., Kaneda K., J. Am. Chem.
Soc., 126, 10657—10666 (2004).
8) Marko I. E., Gautier A., Dumeunier R., Doda K., Philippart F., Brown
S. M., Urch C. J., Angew. Chem. Int. Ed., 43, 1588—1591 (2004).
9) Stahl S. S., Angew. Chem. Int. Ed., 43, 3400—3420 (2004), and refer-
ences cited therein.
10) Iwasawa T., Tokunaga M., Obora Y., Tsuji Y., J. Am. Chem. Soc., 126,
6554—6555 (2004).
7
8
(80)
(56)
9
(Trace)b)
c)
11) Jensen D. R., Schultz M. J., Mueller J. A., Sigman M. S., Angew.
Chem. Int. Ed., 42, 3810—3813 (2003).
10
—
12) Itoh A., Kodama T., Masaki Y., Chem. Lett., 2001, 686—687 (2001).
13) Pavlinac J., Zupan M., Stavber S., J. Org. Chem., 71, 1027—1032
(2006).
a) The yields are for pure, isolated products. b) Most of 17 was recovered.
c) The starting material 19 was recovered quantitatively.
14) Mori N., Togo H., Tetrahedron, 61, 5915—5925 (2005).
15) Mori N., Togo H., Synlett, 2004, 880—882 (2004).
16) Miller R. A., Hoerrner R. S., Org. Lett., 5, 285—287 (2003).
17) A typical procedure follows: A dry ethyl acetate solution (5 ml) of the
4-tert-butylbenzylalcohol (0.3 mmol) and I2 (0.03 mmol) in a Pyrex
test tube equipped with an O2-balloon, was stirred and irradiated at
room temperature for 24 h with four of 22-W fluorescent lamps, which
was set from the test tube in the distance of 80 mm. The reaction mix-
ture was concentrated under reduced pressure, and dissolved in diethyl
ether, and washed with sodium thiosulfate and brine. The organic layer
was dried over Na2SO4, and concentrated under reduced pressure. The
pure product was obtained by preparative tlc.
18) The yield of 2 under air was lower than that under oxygen atmosphere.
19) 2% of 4-chlorobenzoic acid was obtained and 9% of 5 was recovered.
20) The yield of 2 under discontinuous of irradiation was much lower than
that under the usual conditions.
21) Minisci F., Porta O., Recupero F., Punta C., Gambarotti C., Pierini M.,
Galimberti L., Synlett, 2004, 2203—2205 (2004).
Chart 2. Plausible Path of the Aerobic Photo-oxidation of Alcohols
forded by abstraction of a hydrogen radical with iodine (Eq.
4).21) In the case of 17, pyridine ring is assumed to trap a hy-
drogen iodide, and the subsequent reaction, therefore, did not
proceed.