苄基保护氨基

一、保护

苄基（Bn）是最稳定的氨基保护基之一，同PMB一样，对大多数反应都是稳定的，但比PMB更加稳定，因而也更难脱除。酰胺的苄基，常规加氢方法不易脱除，可以通过Na/NH₃脱除。

苄基（Bn）的引入

一般和PMB 一样也采用C6H4CH2Br或C6H4CH2Cl和K2CO3、DIPEA、NaH、Et3N和n-BuLi在有机溶剂(如DMF、二氯甲烷和乙腈等)中反应来引入，或C6H4CHO/NaBH4、NaBH3CN或NaBH(OAc)3还原胺化引入。

烷基化引入苄基(Bn)示例

J. Cossy; I.Pevet et al., Eur. J. Org. Chem., 2001, 15, 2841

AnhydrousK₂CO₃(500 mg, 3.62 mmol, 2.0 equiv.), n-Bu₄NI (66 mg, 0.18mmol, 0.1 equiv.), and benzyl bromide (0.24 mL, 1.98 mmol, 1.1 equiv.) wereadded successively to a solution of compound 1 (500 mg, 1.81mmol) in CH₃CN (5 mL). After 2 h at 35 - 40 °Cand overnight at room temperature, the reaction mixture was diluted with ether,filtered, and concentrated under reduced pressure. The crude material waspurified by flash chromatography (cyclohexane - AcOEt, 95:5 to 90:10) to give compound2 (0.54 g, 81%) as a colorless oil. [α]_D²⁰= +12.9 (c =1.99, CHCl₃).

 还原胺化引入苄基（Bn）示例

Rompaey, Karolien Van;Eynde, Isabelle Van den et al., Tetrahedron,2003, 59(24), 4421-4432

Compound 1 (0.5 g, 1.70 mmol) was dissolved in 1,2-dichloroethane(50 mL) and the aldehyde (0.122 g,1.70 mmol), Et₃N (0.172 g,1.70 mmol), NaBH(OAc)₃ (0.505 g,2.38 mmol) and MgSO₄(30wt%) were added. The reaction was stirred at room temperature. RP-HPLCindicated reaction times between 2 and 4 h. The mixture was quenched with saturatedNaHCO₃(50mL) and extracted with EtOAc (3 x 70 mL). The organiclayer was dried (MgSO₄), filtered and evaporated to give compound 2, which were used without furtherpurification.

二、去保护

Bn常用催化氢解脱去，如H₂/20%Pd(OH)₂-C 、H₂/Pd-C 、H₂/PdCl₂ 、Pd/HCOOH或Pd-C/HCOOH、Pd-C/HCOONH₄、Pd-C/NH₂NH₂或Pd-C/环已烯作氢源转移氢化，而用H₂/Pd-C去保护通常很慢，除非添加Boc₂O促进Bn的离去。另外CCl₃CH₂COCl/CH₃CN、Li/MH₃、Na/NH₃、CAN和CH₃CHClOCOCl也经常应用。酰氨上的苄基一般较难用氢解脱除，此时可以用AlCl₃进行脱除。

一、H₂/Pd-C氢化脱苄基(Bn)示例

Basso, Andrea; Banfi, Luca et al., J. Org. Chem., 2005, 70(2),575-579

A mixture of compound1 (1.5 g, 2.4mmol) and 10% Pd/C (300 mg) in methanol (40 mL) was stirred overnight under H₂(3bar). The reaction mixture was filtered over Celite, and the filtrate wasconcentrated in vacuo. Compound 2 (1.07 g) was obtained as a pale yellow oil in quantitativeyield.

二、HCOONH₄/Pd-C氢化脱苄基(Bn)示例

Tilekar, Jayant N; Patil, Nitin T et al., Tetrahedron, 2003, 59(11), 1873-1876

A solution of compound 1(1.1 g, 2.75 mmol), ammoniumformate (0.92 g, 15.1mmol) and 10% Pd–C (0.2 g) inmethanol (10 mL) was refluxed for 40 min. The catalyst was filtered throughcelite and washed with methanol (5 mL x 2). To the filtrate,cooled to 0°C was added sodium bicarbonate (0.725 g, 8.61 mmol) and benzyloxycarbonylchloride (0.47 g, 2.70mmol) and the stirred reaction mixture warmed to room temperature. After 2 h,methanol was removed under reduced pressure and the residue was extracted withethyl acetate (5 mL x 3). Combined extract was washed with brine, dried overanhydrous sodium sulphate and concentrated on rotovapor to afford a residue whichwas purified by column chromatography (chloroform/methanol, 9/1) to givecompound 2 (0.81 g, 84%)as a thick liquid; R_f(20%methanol/chloroform) 0.6; [α]_D =+18.02 (c = 0.20, CHCl₃).

三、ClCOOCH₂CCl₃脱苄基(Bn)示例

V. H. Rawal, R. J.Jones et al., J. Org. Chem., 1987, 52, 19

To compound 1 (2.30 g, 6.8 mmol) inacetonitrile (25 mL) was added trichloroethyl chloroformate (0.100 mL, 6.8mmol). The mixture was stirred for 30 min and concentrated. The crude productwas chromatographed (hexanes:methylene chloride = 1:l) to yield compound 2 (2.68 g, 93%) as a white needles, whichcrystallized from absolute ethanol: mp 162.5 °C.

To a solution of compound 2(1.40 g, 3.3 mmol) in acetic acid (30 mL) wasadded powdered zinc (0.5 g) inportions over a period of 2 h. The reaction was filtered, and the precipitate waswashed thoroughly with methylene chloride. The filtrate was concentrated andextracted with ether. The organic layer was neutralized with saturated sodiumbicarbonate solution and dried (Na₂SO₄). The crudeproduct was concentrated and chromatographed (methylene chloride:ether = 10:1) to yield compound3(0.72 g, 88%) asa yellow oil, which gradually crystallized: mp 103-104°C.

四、 Na/NH3脱苄基(Bn)示例

Wang, Xiaodong J; Hart, Scott A et al., J. Org. Chem., 2003,68(6), 2343-2349

NH₃(ca. 160 mL) was distilled into 40 mL of THF at -78 °C and allowed to warm to reflux (-33 °C). Na (ca. 2.0 g, 87mmol) was added until a deep blue solution was sustained. A solution of acid 1(2.0 g, 4.3 mmol) in THF (10mL) was added directly to the Na/NH₃ solution slowly via cannula overca. 5 min. After being stirred for 45 min at reflux, the reaction was quenchedwith NH₄Cl (10 mL) and then allowed to warm to rt with concentration to ca. 30 mL(caution! NH₃evolved). The mixture was diluted with NH₄Cl (50 mL),acidified with 1 N HCl to pH 7, and extracted with CHCl₃(10 x 50 mL), dried on MgSO₄, and concentrated to give 810 mg(66%) of the alcohol 2 as a pale yellow oil (further purification can beachieved by chromatography on silica with 3% MeOH in CHCl₃if desired).

4.4.2.5  CAN脱苄基(Bn)示例

Bull, Steven D;Davies, Stephen G et al., J. Chem. Soc.Perkin Trans. 1, 2001, 23,3106-3111

CAN (3.9 g, 7.1 mmol) was added portionwise to a stirredsolution of 24 (1.0 g,2.54 mmol) in MeCN-H₂O (30 mL, 5:1) and stirred at RT. After sixteen hours,the reaction was quenched by the addition of saturated aqueous sodiumbicarbonate solution and stirred vigorously for ten minutes before extractionwith Et₂O. The combined organic extracts were dried (MgSO₄), filtered and concentrated in vacuo before purification by column chromatography on silica gel (hexane-Et₂O = 5 : 1 and 1%Et₃N) gave 25 (562 mg, 73%) as a colourless oil; [α]²⁴_D= - 58.6 ( c=1.05, CHCl₃).

CAN选择脱苄基(Bn)示例2

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Bull, Steven D; Davies, Stephen G et al., J.Chem. Soc. Perkin Trans. 1, 2000,22, 3765-3774

CAN (190 mg, 0.35 mmol) was addedportionwise to a stirred solution of compound 1 (90 mg, 0.17 mmol) inMeCN-H₂O (5 : 1, 5 mL) and stirred at RT. The reaction was quenched by the additionof saturated aqueous sodium bicarbonate solution and stirred vigorously for tenminutes before extracting with Et₂O. The combined organic extracts were dried (MgSO₄), filtered and concentrated in vacuo efore purification by column chromatography on silica gel (gradientelution, 30-40 petrol-Et₂O 7: 3 to 1 : 1) to give compound 2 (68 mg, 91%) asa gum. [α]_D²⁴= - 8.3 (c = 1.2, CHCl₃).

六、CH3CHClOCOCl脱苄基(Bn)示例

US6410592：该方法也可用于脱甲基

To a solution of compound 1 (727 mg) in dichloromethane (75ml) which was being maintained at 0 °C under nitrogen was added 1-chloroethylchloroformate (0.208 ml) dropwise.The mixture was then allowed to warm to room temperature, before being heatedto reflux. After approximately 2 h analysis of the reaction mixture indicatedcomplete consumption of the starting material. The dichloromethane wasevaporated and the residue was then taken up into methyl alcohol and heated toreflux for 1 h. The solvent was evaporated to afford the compound 2 (481 mg, 85%), whichwas used in the next reaction with out further purification.

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