alcohols do not react), the route is generally applicable to the
synthesis of a host of dioxane ring functionalized thiophenes.
The reaction was further explored by employing 1,3-alkane-
diols where the 7-membered dioxy ring is furnished by the
reaction. The reaction of 3 with 1,3-propanediol (6a) proceeded
smoothly under Mitsunobu conditions to give the corresponding
product 7a in excellent yield (92%) as shown in Scheme 2.
Again, a systematic study was carried out to investigate the
effect of increasing the steric environment of the diol employed
in the reaction. Subjecting primary alcohols 6b, 6c, and 6d to
the reaction conditions gave the product in high yields (ca.
80–85%). It should be noted that compounds 7b, 7c, and 7d
have never been successfully prepared using the Williamson
etherification route.
In conclusion, we have demonstrated that the reaction of 3
with various 1,2 or 1,3-diols under mild Mitsunobu conditions
gives the corresponding cyclized products in good to excellent
yields. The new method yields monomer precursors with a
variety of substituents on the dioxane ring which are otherwise
difficult to be introduced and avoids the use of environmentally
unfavorable dihaloalkanes. In connection with this study, the
investigation of optically active and further functionalized
dioxythiophenes, along with dioxypyrroles, is in progress.
Notes and references
†
Experimental procedure: In a typical procedure, to a solution of 3 (1.0
equiv.), diol (1.0 equiv.), and PBu3 (2.0 equiv.) in dry THF was dropwise
added diethyl azodicarboxylate (2.4 equiv.) under argon at room tem-
perature. The reaction mixture was stirred for 1 h and stirred at reflux for
6–12 h. The reaction was cooled and THF was removed by a rotary
evaporator. The residue was diluted with ether and stood for crystallization
of tributylphosphine oxide for 12 h. Tributylphosphine oxide was filtered
off and the filtrate was concentrated. Purification of the residue by
chromatography on silica gel using hexane/ethyl acetate (3+1) as an eluent
afforded the desired product. All compounds were fully characterized by 1H
NMR, 13C NMR, HRMS, and elemental analysis. Results for previously
unreported compounds are as follows.
Spectroscopic data of selected compounds: 5b: a colorless solid; mp 130
°C; 1HNMR (300 MHz, CDCl3) d 4.58 (dd, J = 12.0, 2.0 Hz, 1H), 4.53 (q,
J = 7.0 Hz, 4H), 4.38 (m, 1H), 4.23 (dd, J = 12.0, 7.6 Hz, 1H), 2.10–1.85
(m, 2H), 1.55 (t, J = 7.0 Hz, 3H), 1.54 (t, J = 7.0 Hz, 3H), 1.31 (t, J = 7.3
Hz, 3H); HRMS (FAB) calcd for C14H18O6S (MH+) 315.0902, found
315.0902; Anal. Calcd for C14H18O6S: C, 53.49; H, 5.77; S, 10.20. Found:
1
C, 53.53; H, 5.80; S, 10.21%. 5c: a colorless solid; mp 105 °C; H NMR
(300 MHz, CDCl3) d 4.45 (q, J = 6.6 Hz, 2H), 4.32 (q, J = 7.1 Hz, 4H),
1.38 (d, J = 7.0 Hz, 6H), 1.37 (t, J = 7.1 Hz, 6H); HRMS (FAB) calcd for
C14H18O6S (MH+) 315.0902, found 315.0902; Anal. Calcd for C14H18O6S:
C, 53.49; H, 5.77; S, 10.20. Found: C, 53.43; H, 5.72; S, 10.22%. 5d: a
colorless solid; mp 89–90 °C; 1HNMR (300 MHz, CDCl3) d 4.40 (m, 1H),
4.33 (q, J = 7.0 Hz, 4H), 4.29 (m, 1H), 4.03 (dd, J = 11.3, 7.6 Hz, 1H), 1.58
(t, J = 7.2 Hz, 2H), 1.36 (t, J = 6.8 Hz, 6H), 1.23–130 (m, 16H), 0.86 (t,
J = 6.7 Hz, 4H). 7c: a colorless solid; mp 100 °C; 1H NMR (300 MHz,
CDCl3) d 4.20 (q, J = 7.1 Hz, 4H), 4.15 (s, 4H), 1.42 (q, J = 7.5 Hz, 4H),
1.35 (t, J = 7.1 Hz, 6H), 0.85 (t, J = 7.5 Hz, 6H); HRMS (FAB) calcd for
C17H24O6S (MH+) 357.1372, found 357.1372; Anal. Calcd for C17H24O6S:
C, 57.28; H, 6.79; S, 9.00. Found: C, 57.20; H, 6.78; S, 9.02%. 9: a colorless
thick oil; 1H NMR (300 MHz, CDCl3) d 4.70–4.50 (m, 1H), 4.41–4.21 (m,
4H), 4.22–4.12 (m, 1H), 2.22–1.95 (m, 2H), 1.46 9d, J = 6.3 Hz, 3H), 1.43
(d, J = 6.3 Hz, 3H), 1.34 (t, J = 7.1 Hz, 3H), 1.33 (t, J = 7.1 Hz, 3H);
HRMS (FAB) calcd for C15H20O6S (MH+) 329.1059, found 329.1059;
Anal. Calcd for C15H20O6S: C, 54.86; H, 6.14; S, 9.76. Found: C, 54.80; H,
6.17; S, 9.80%.
Scheme 2 Propylenedioxythiophene derivative formation via Mitsunobu
chemistry.
Increasing the steric congestion further as shown in Scheme
3, subjection of 2,4-pentanediol (8, isomer mixture) to the
Mitsunobu reaction gave the 1,3-dimethylProDOT (9) in 60%
yield. With the above examples, it is demonstrated that the
method developed here is useful for the synthesis EDOT and
ProDOT derivatives with a wide variety of substituents.
1 Handbook of Conducting Polymers, 2nd ed., ed. T. A. Skotheim, R. L.
Elsenbaumer and J. R. Reynolds, Marcel Dekker, New York, 1998.
2 (a) Z. Bao and A. J. Lovinger, Chem. Mater., 1999, 11, 2607; (b) W. Li,
H. E. Katz, A. J. Lovinger and J. G. Laquindanum, Chem. Mater., 1999,
11, 458.
3 (a) O. Ingänas, in Organic Electroluminescent materials and Devices, ed.
S. Miyata, H. S. Nalwa, Gordon and Breach Publishers, Amsterdam,
1997, pp. 147–175; (b) Y. Kaminovz, E. Smela, T. Johansson, L.
Brehmer, M. R. Anderson and O. Ingänas, Synth. Met., 2000, 113,
103.
4 P. Skabara, Chem. Ind., 2001, 12, 371.
5 B. C. Thompson, P. Schottland, K. Zong and J. R. Reynolds, Chem.
Mater., 2000, 12, 1563.
Scheme 3 Sterically hindered ProDOT formation.
To confirm the usefulness of these intermediates in preparing
new monomers for electroactive and conducting polymer
formation, compound 7c was hydrolysed and decarboxylated to
yield 2,2A-diethyl substituted ProDOT (10) in 70% overall yield
as shown in Scheme 4.
6 L. Groenendaal, F. Jonas, D. Freitag, H. Pielartzik and J. R. Reynolds,
Adv. Mater., 2000, 12, 481.
7 A. Kumar, D. M. Welsh, M. C. Morvant, K. Abboud and J. R. Reynolds,
Chem. Mater., 1998, 10, 896.
8 D. M. Welsh, A. Kumar, E. W. Meijer and J. R. Reynolds, Adv. Mater.,
1999, 11, 1379.
9 (a) O. Mitsunobu, Synthesis, 1981, 1–28; (b) C. Ahn, R. Correia and P.
DeShong, J. Org. Chem., 2002, 67, 1751; (c) C. Ahn and P. DeShong, J.
Org. Chem., 2002, 67, 1754; (d) J. S. Bajwa and R. C. Anderson,
Tetrahedron Lett., 1990, 31, 6973; (e) T. Tsunoda, F. Ozaki, N. Shirakata,
Y. Tamaoka, H. Yamamoto and S. Ito, Tetrahedron Lett., 1996, 37, 2463;
(f) P. A. Aristoff, A. W. Harrison and A. M. Huber, Tetrahedron Lett.,
1984, 25, 3955.
Scheme 4 Diethyl ProDOT formation from Mitsunobu derived precursor.
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