钯催化硼-碳和硼-杂原子键构建一锅法合成双官能团化邻-碳硼烷※

doi:10.6023/A21120597

摘要/Abstract

碳硼烷是由碳氢和硼氢顶点组成的笼状分子, 在医药、能源和材料等领域有着重要应用, 但目前在碳硼烷硼顶点引入杂原子取代基的方法还较为有限. 基于此, 本工作从3-碘-邻-碳硼烷出发, 通过钯催化烯基化、金属迁移及后续与杂原子亲核试剂的偶联反应, 一锅法构筑硼碳键和硼杂原子键, 成功实现了一系列新型3-烯基-4-胺基/烷氧基/烷(芳)硫基-邻-碳硼烷衍生物的合成.

关键词: 碳硼烷, 钯催化, 金属迁移, 硼-碳键, 硼-杂原子键

Icosahedral carboranes are carbon-boron molecular clusters, sharing many features with benzene such as aromaticity, high thermal and chemical stability. On the other hand, carboranes have their own unique characteristics like spherical geometry and three-dimensional electronic delocalization. These properties render carboranes unique building blocks for various applications ranging from versatile ligands to functional materials to medicine. In this regard, functionalization of carboranes, particularly regioselective functionalization of cage B-vertexes has recently received much attention. Based on our recently developed Pd-catalyzed iodine-migration on o-carborane cage, a Pd-catalyzed regioselective difunctionalization of 3-iodo-o-carborane in a one-pot manner has been achieved to afford a series of 3-alkenyl-4-Nu-o-carboranes (Nu=arylamino, alkoxyl, alkyl and arylthio) in 47%~99% yields. This protocol combines the sequential activation of cage B(3)—I and B(4)—H bonds by Pd migration, as well as further Pd-catalyzed transformation of B(4)—I bond, leading to the construction of B—C and B—Heteroatom bonds. A general procedure for the synthesis of 3-alkenyl-4-Nu-o-carboranes is described as follows: to a tetrahydrofuran (THF) solution (1 mL) of NuH (1.0 mmol) was added base (1.0 mmol) at 0 ℃ under an atmosphere of dry nitrogen. The reaction mixture was stirred for another 10 min to obtain the NuM solution (NuM=ArNHMgBr, base=EtMgBr; NuM=Ar₂NLi, base=ⁿBuLi). Another oven-dried Schlenk flask equipped with a stir bar was charged with 3-iodo-o-carborane (1, 27 mg, 0.1 mmol), Pd(PPh₃)₄ (12 mg, 0.01 mmol), diphenylacetylene (89 mg, 0.5 mmol) and dry toluene (1 mL) under an atmosphere of dry nitrogen. The flask was closed, and stirred at 80 ℃ for 72 h. Then, the resulting solution was cooled to 0 ℃, to which was slowly added NuM (0.15 mmol) (NuM=ArNHMgBr, Ar₂NLi, ^tBuONa and RSNa). The reaction mixture was warmed to room temperature, and stirred at 80 ℃ for 24 h. After quenching with water (1 mL) and extraction with ethyl acetate (5 mL×3), the organic portions were combined and concentrated to dryness in vacuo. The residue was subjected to flash column chromatography on silica gel (300~400 mesh) using n-hexane as eluent to give the product.

Key words: carborane, palladium catalysis, metal migration, B—C bond, B—Heteroatom bond

引用此文

葛懿修, 邱早早, 谢作伟. 钯催化硼-碳和硼-杂原子键构建一锅法合成双官能团化邻-碳硼烷^※[J]. 化学学报, 2022, 80(4): 432-437.

Yixiu Ge, Zaozao Qiu, Zuowei Xie. Pd-Catalyzed One-Pot Synthesis of Difunctionalized o-Carboranes via Construction of B—C and B—Heteroatom Bonds^※[J]. Acta Chimica Sinica, 2022, 80(4): 432-437.

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图/表 11

图1. 钯催化3-卤代-邻-碳硼烷的B—Heteroatom键构建

Figure 1. Palladium catalyzed B—Heteroatom bond construction from 3-halo-o-carborane

Entry	R	[M]	equiv. of 3
1	H	Li	1.5	49
2	H	Li	4.0	—^c
3	H	Na	1.5	44
4	H	MgBr	1.5	87 (74)^d
5	H	MgBr	1.2	75
6	H	MgBr	2.0	73
7	H	MgBr	3.0	69
8	Ph	Li	1.5	55
9^e	Ph	Li	1.5	60 (47)^d
10	Ph	MgBr	1.5	N.R.

表1. 一锅法构筑B—C键和B—N键反应的条件筛选a

Table 1. Optimization of reaction conditions for one-pot construction of B—C and B—N Bonds

Entry	R¹	R²	4	Yield^b/%
1	Ph	H	4a	74
2^c	o-Me-C₆H₄	H	4b	58
3	m-Me-C₆H₄	H	4c	65
4	p-Me-C₆H₄	H	4d	82
5^c^,^d	p-MeO-C₆H₄	H	4e	61
6	p-F-C₆H₄	H	4f	75
7	p-CF₃-C₆H₄	H	—	N.R.
8	2-Nap	H	4g	83
9	4-Py	H	—	N.R.
10	^tBu	H	—	Messy
11	Bn	H	—	Messy
12	Ph	Ph	4h	47
13	p-MeO-C₆H₄	p-MeO-C₆H₄	4i	51
14	Ph	p-F-C₆H₄	4j	60

表2. 一锅法合成3-烯基-4-胺基-邻-碳硼烷a

Table 2. Substrate scope for one-pot synthesis of 3-alkenyl-4-amino-o- carboranes

图2. 4a的分子结构

Figure 2. Molecular structure of 4a

图3. 4d的分子结构

Figure 3. Molecular structure of 4d

图4. 4h的分子结构

Figure 4. Molecular structure of 4h

Entry	RO[M]	6	Yield^b/%
1	PhONa	—	N.R.
2	PhOMgBr	—	N.R.
3	MeONa	—	—^c
4^d	^tBuONa	6a	51

表3. 一锅法构筑B—C键和B—O键a

Table 3. One-pot construction of B—C and B—O bonds

图5. 6a的分子结构

Figure 5. Molecular structure of 6a

Entry	R	8	Yield^b/%
1^c	Me	8a	99
2^c	Et	8b	81
3^c^,^d	ⁱPr	8c	77
4	Ph	8d	99
5	p-MeO-C₆H₄	8e	62
6	p-F-C₆H₄	8f	66
7	p-CF₃-C₆H₄	—	N.R.

表4. 一锅法构筑B—C键和B—S键a

Table 4. One-pot construction of B—C and B—S bonds

图6. 8a的分子结构

Figure 6. Molecular structure of 8a

图7. 金属迁移及硼-杂原子偶联反应机理

Figure 7. Metal migration and B—heteroatom coupling reaction mechanism

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