1、Me3SiI
另一種常用的去甲基試劑，在此體系中，雙鍵、三鍵、酮羰基、氨基和鹵代物穩(wěn)定，但芐醚、三苯甲基醚、叔丁基醚不穩(wěn)定。三甲基碘硅烷能裂解酯但比醚慢。
范例：
Table 1. Dealkylation of Ethers by Trimethylsilyl Iodide
a) Solvent CDCl 3 , unless otherwise mentioned. b) In CCl 4 .
General Procedure for Dealkylation of Ether. To a 2 M solution of ether (1 equiv.) in asuitable solvent (Table 10) is added neat trimethylsilyl iodide (1.3 equiv.) through a dry syringe. The reaction is maintained at temperature indicated in Table 10 and monitored by NMR for completion. Yields are calculated by NMR integration of pertinent peaks. For isolation of the alcohols, at the completion of the reaction, the excess trimethylsilyl iodide is destroyed and the intermediate trimethylsilyl ether formed during the reaction is hydrolyzed to alcohol by pouring the reaction mixture into methanol (4 equiv.). The volatile components are removed at reduced pressure and the residue is taken up in ether, washed with aqueous sodium bisulfite, aqueous sodium bicarbonate and brine and dried. The residue left after evaporation of solvent is further purified (if necessary) by column chromatography on silica gel.
2、LiCl/DMF
當(dāng)鄰位和對(duì)位有吸電子基團(tuán)存在時(shí)，此體系去甲基化容易進(jìn)行。底物中有醛和酯時(shí)，去甲基需更長(zhǎng)的時(shí)間，甲酯會(huì)去甲基形成酸。
范例：
Table 12. Cleavage of Alkyl Aryl Ethers with LiCl in DMF
Typical Procedure. Cleavage of 2,3-Dimethoxybenzaldehyde.
2,3-Dimethoxybenzaldehyde (1.0 g, 6 mmol) and LiCl (0.76 g, 18 mmol) are heated in boiling DMF (10 mL), the reaction being monitored by GLC. When the starting material disappears, 10% aqueous NaOH (30 mL) is added; the solution is washed with ether (2×25mL), then acidified with 10% aqueous HCl (50 mL), and extracted with ether (2×25 mL).The organic phase is washed with brine (30 mL), dried (sodium sulfate) and concentrated in arotary evaporator to afford 2-hydroxy-3-methoxybenzaldehyde (0.88 g, 98%).
3、吡啶鹽酸鹽
將底物和大大過(guò)量的吡啶鹽酸鹽混合均勻，加熱到 200℃左右進(jìn)行，反應(yīng)完后，常規(guī)后處理即可
范例：
Demethylation of p-Dihydrothebainol Methyl Ether with Pyridine Hydrochloride.
A mixture of 204 mg. of β-dihydrothebainol methyl ether and 247 mg. of freshly fused pyridine hydrochloride was heated for four hours at 195- 00' (bath). The cooled brownish residue was dissolved in water, niade basic with potassium hydroxide containing hydrosulfite, and extracted several times with chloroform. The chloroform, after processing, was found to contain only a trace of non-volatile residue. The aqueous alkaline layer was then carbonated o excess and extracted several times with butanol. The butanol extracts were washed, filtered through anhydrous sodium sulfate, and concentrated under nitrogen. Crystallization occurred during the concentration, and the residue melted at 239-242' dec. (162 ing.). Several crystallizations from butanol gave 72 mg. of small prisms, m.p. 258-262" dec., [a]%D 1-46'( c 1.32, diox .).
