No.107
Mild and Selective Reagents
for Cleavage of Protecting Groups
for Cleavage of Protecting Groups
| B2132 | B-Bromocatecholborane (1a) |
5g |
| C1669 | B-Chlorocatecholborane (1b) |
5g |
The reagents 1, which are Lewis acids, selectively cleave certain ether, ester and carbamate protecting groups under mild conditions.1) The relative reactivity of common protecting groups towards 1 was reported:1a) MOMOR, MEMOR > BOC > CBZ, tBuOR > PhCH2OR > CH2=CHCH2OR > tBuO2CR, secondary alkylOR > PhCH2O2CR, primary alkylOR >> alkylO2CR. The reagent 1b, which has lower reactivity than 1a, may be advisable when higher selectivity is required, for example, synthesis of natural products. Additionally, TBDMS, TBDPS and PMB ethers are not affected by 1.2)
MOM = Methoxymethyl
MEM = 2-Methoxyethoxymethyl
Boc = tert-Butoxycarbonyl
Cbz = Benzyloxycarbonyl
TBDMS = tert-Butyldimethylsilyl
TBDPS = tert-Butyldiphenylsilyl
PMB = p-Methoxybenzyl
References
1) Mild and selective reagents for cleavage of ether, ester, and carbamate protecting groups
a) R. K. Boeckman, Jr., J. C. Potenza, Tetrahedron Lett., 26, 1411 (1985).
b) P. F. King, S. G. Stroud, ibid., 26, 1415 (1985).
2) Synthesis of prostaglandin F2α photoaffinity probes
M. Golinski, M. Heine, D. S. Watt, Tetrahedron Lett., 32, 1553 (1991).
3) Synthetic studies on spinosyn A.
L. A. Paquette, Z. Gao, Z. Ni, G. F. Smith, Tetrahedron Lett., 38, 1271 (1997).
a) R. K. Boeckman, Jr., J. C. Potenza, Tetrahedron Lett., 26, 1411 (1985).
b) P. F. King, S. G. Stroud, ibid., 26, 1415 (1985).
2) Synthesis of prostaglandin F2α photoaffinity probes
M. Golinski, M. Heine, D. S. Watt, Tetrahedron Lett., 32, 1553 (1991).
3) Synthetic studies on spinosyn A.
L. A. Paquette, Z. Gao, Z. Ni, G. F. Smith, Tetrahedron Lett., 38, 1271 (1997).
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