吡啶-2-甲酸酯保护羟基（可中性条件下去保护）
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上保护：
一、通过Mitsunobu反应条件制备醇的吡啶-2-甲酸酯。
Typical experimental procedure for the Mitsunobu reaction: A 25 mL round bottom flask was charged with picolinic acid (312 mg, 2.53 mmol), menthol (99 rag, 0.634 retool), and triphenylphosphine (664 mg, 2.53 mmol). The flask was flushed with nitrogen, and THF (7 mL, freshly distilled from Na) was added, and the solution cooled to -20°C (20% aqueous CaCI2/CO2 bath) for 10-15 min. Diisopropyl azodicarboxylate (DIAD, 499 lxL, 2.53 retool) was then added dropwise to the solution over 3 rain. The temperature of the bath was maintained at -20 to -25°C for 4.5 h, and the cold bath allowed to slowly warm to ambient temperature and allowed to stir overnight. The reaction mixture was then concentrated at reduced pressure, and the products were purified by flash chromatography (the crude mixture was applied to the column using a minimal amount of CH2C12 and eluted with hexanes then 5:1 hexanes / ethyl acetate) to provide the picolinate ester of neomenthol (132 mg, 0.505 mmol, 80%).
【Tetrahedron Letters, 1999, 40, 2685-2688】
二、吡啶-2-甲酰氯盐酸盐（CAS号：39901-94-5）已经商业化，可以直接买到，醇，picolinoyl chloride (1.2 equiv)，三乙胺，在二氯甲烷中反应，产率 83–97% 。
【(a) Chem. Commun. 2005, 933; (b) Tetrahedron Lett. 2005, 46, 2299; (c) Tetrahedron 2005, 61, 1289; (d) J. Org. Chem. 2005, 70, 837; (e) Org. Lett. 2004, 6, 2693; (f) Synth. Commun. 2004, 35, 941; (g) Org. Lett. 2003, 5, 4755; (h) Eur. J. Org. Chem. 2003, 4121; (i) Synlett 2002, 1919; (j) Chem. Commun. 2002, 1036.】
脱保护
Typical experimental procedure for the methanolysis of picolinate esters: A 10 mL round bottom flask was charged with CHCI3 (3 mL), ester 11 (Table 2, entry 3, 91 mg, 0.253 retool), methanol (89 uL, 2.08 mmol) and Cu(OAc)2 (23 mg, 0.126 mmol). The reaction was allowed to stir for 6 h at which point it was judged complete by TLC. The reaction was diluted with hexanes (1 ml) and washed with disodium
EDTA (lml of a 0.1 M solution). The organic layer was dried (MgSO4), filtered, and concentrated to an oil. Flash chromatography (hexanes then 5:1 hexanes / ethylacetate) provided the corresponding β-hydroxyketone (55 mg, 0.223 mmol, 85%).
【Tetrahedron Letters, 1999, 40, 2685-2688】
二、Zn(OAc)2, 二氯甲烷/甲醇中，室温下反应1.5到4小时，89-97%收率。可选择性脱去糖的2-位羟基的保护基。
一系列化合物的脱保护都取得很好的反应产率。
Typical procedure for deprotection : A solution of 2a (48 mg, 0.20 mmol) and Zn(OAc)2-2H2O (44 mg, 0.20 mmol) in CH2Cl2 (1.9 mL) and MeOH (0.1 mL) was stirred for 100 min at room temperature. The reaction mixture was quenched with saturated aqueous NH4Cl (1 mL) and diluted with CH2Cl2 (10 mL). The organic layer was washed with 1 N aqueous HCl solution (5 mL · 2) and brine to remove methyl picolinate, then it was dried over MgSO4, and concentrated to give the pure parent alcohol 1a (26 mg, 96%).