Chemistry Letters 2002
153
CH3CO2H ꢂ CF3CO2H ꢂ CH3SO3H < CF3SO3H (entries 1–
6). Second, allyltributylstannane was found to be a more effective
precursor than tributylstannane, and the desired stannyl ethers
formed in excellent yields (entries 8 and 9). Third, the current
method was generally applicable for primary, secondary and
tertiary alcohols, though the stannyl ether derived from t-butyl
alcohol did not give the acylated product but instead gave the t-
butyl chloride quantitatively (entry 7).11 Finally, when 0.2 equiv
of the acid catalyst was used, very slow conversion sometimes
resulted; however the useof 0.3 equiv of the acid catalyst gaverise
to satisfactory and reproducible conversion to the desired stannyl
ether within 1 h in quantitative yield (entry 10).
As the formation of the stannyl ether takes place under mild
conditions, the current method could be successfully applied to
glycosylation reactions (Scheme 2). Thus, the coupling of methyl
tributylstannyl ether prepared by the present protocol with ꢀ-
bromoglycoside 2A6 proceeded smoothly to give the orthoester 3.
While the acid labile orthoester 3 was not affected by Bu3SnOTf
that was present in the reaction medium,12 it was converted to the
O-glycoside 4 by the action of TMSOTf.
the reaction conditions.
In summary, we have developed a new method for the
synthesis of stannyl ethers from alcohols under very mild
conditions, which are compatible with a variety of acid- and
base-labile functional groups. Further synthetic investigation is
underway and will be reported in due course.
This work was partly supported by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Science,
Sports, and Culture, Japan.
This paper is dedicated to Professor Teruaki Mukaiyama on
the occasion of his 75th birthday.
References and Notes
1
a) S. David, in ‘‘Preparative Carbohydrate Chemistry,’’ ed. by S.
Hanessian, Marcel Dekker, Inc., New York (1997), Chap. 4. b)
A. G. Davis, in ‘‘Organotin Chemistry,’’ VCH, Weinheim (1997),
Chap. 12. c) M. Pereyre, J.-P. Quintard, and A. Rahm, in ‘‘Tin in
Organic Synthesis,’’ Butterworths, London (1987), Chap. 4. d) Y.
Tsuda, J. Syn. Org. Chem. Jpn., 55, 907 (1997). e) S. David and S.
Hanessian, Tetrahedron, 41, 643 (1985). f) C. Cruzado, M.
´
Bernabe, and M. M.-Lomas, J. Org. Chem., 54, 465 (1989).
2
3
4
T. W. Greene and G. M. Wuts, in ‘‘Protective Groups in Organic
Synthesis,’’ John Wiley & Sons, Inc., New York (1999), Chap. 2.
´
B. Herradon, A. Morcuende, and S. Valverde, Synlett, 1995, 455
and references therein.
While elegant applications of stannyl ethers in organic synthesis
have recently appeared, all have dealt with 1,2-diol systems. See
recent examples: F. Iwasaki, T. Maki, O. Osamura, W. Nakashima,
and Y. Matsumura, J. Org. Chem., 65, 996 (2000); E. Kaji, and N.
Harita, Tetrahedron Lett., 41, 53 (2000); R. Martinez-Bernhardt,
´
P. P. Castro, G. Godjoian, and C. G. Gutierrez, Tetrahedron, 54,
8919 (1998); G. Hodosi and P. Kovac, Carbohyd. Res., 308, 63
´
´
(1998); G. Hodosi and P. Kovac, J. Am. Chem. Soc., 119, 2335
(1997); K. C. Nicolaou, F. L. van Delft, S. R. Conley, H. J.
Mitchell, Z. Jin, and R. M. Rodriguez, J. Am. Chem. Soc., 119, 9057
(1997); S. J. Danishefsky, J. Gervay, J. M. Peterson, F. E.
McDonald, K. Koseki, D. A. Griffith, T. Oriyama, and S. P.
Marsden, J. Am. Chem. Soc. 117, 1940 (1995).
5
6
7
T. Mukaiyama, J. Ichikawa, and M. Asami, Chem. Lett., 1983, 293;
J. Ichikawa, M. Asami, and T. Mukaiyama, Chem. Lett., 1984, 949.
S. Yamago, T. Yamada, O. Hara, H. Ito, Y. Mino, and J. Yoshida,
Org. Lett., 3, 3867 (2001).
a) A. K. Sawyer and H. G. Kuivila, J. Org. Chem., 41, 610 (1962);
´
b) Y. T. Xian, P. Four, F. Guibe, and G. Balavoine, Nouv. J. Chim.,
8, 611 (1984).
A. Saitow, E. G. Rochow, and D. Seyferth, J. Org. Chem., 23, 116
(1958).
X. Kong, T. B. Grindley, P. K. Bakshi, and T. S. Cameron,
Organometallics, 12, 4881 (1993).
Scheme 2. Reaction conditions: i) Allyl tribuytin (1.3 equiv),
CF3SO3H (0.3 equiv), CH2Cl2, rt, 2 h. ii) 2A (1.0 equiv), 0 ꢃC, 1 h.
iii) TMSOTf (0.1 equiv), 0 ꢃC, 0.1 h. iv) 2B (1.5 equiv), r.t., 0.5 h,
then TMSOTf (0.1 equiv), 0 ꢃC, 0.1 h. v) 2C (1.5 equiv), r.t., 0.5 h,
then TMSOTf (0.1 equiv), 0 ꢃC, 0.1 h.
8
9
We next examined the glycosidation reactions of the
glycosides 5 and 7 in order to examine the functional group
compatibility of the present method. We were very pleased to find
that the base labile acetyl group and the acid labile acetal and
arylselenyl groups in 5 and 7 were completely inert under the
reaction conditions, and that the coupling reaction of tributyl-
stannyl ethers 5b and 7b with 2B or 2C gave the corresponding
disaccharides 6 and 8, respectively, in good yields. Several
attempts to prepare 5b by conventional methods from 5a with
(Bu3Sn)2O or Bu3SnOMe in benzene under reflux were
unsuccessful due to the instability of the acetyl groups under
10 While pure tributylstannyl methyl ether gives a sharp signal at
108 ppm (ꢁꢂ1=2 ¼ 15 Hz), addition of 0.2 equiv of trifluorometha-
nesulfonic acid resulted in a lower field shift with considerable line
broadening (112 ppm, ꢁꢂ1=2 ¼ 149 Hz).
11 t-Butyl alcohol and benzoyl chloride did not give t-butyl chloride
under similar conditions. Therefore, the t-butyl chloride must be
formed by way of the corresponding stannyl ether.
12 The result clearly revealed that the reactivity of tributyltin
methoxide prepared by the current method, which contains
tributyltin triflate, and that of commercially available one without
such contaminant was identical.