Huang Kexuan, Martin Caleb D
Baylor University , Department of Chemistry and Biochemistry, One Bear Place 97348, Waco, Texas 76798, United States.
Inorg Chem. 2015 Feb 16;54(4):1869-75. doi: 10.1021/ic502784d. Epub 2015 Jan 17.
Reactions of pentaphenylborole with isocyanates, benzophenone, and benzaldehyde produced new seven-membered heterocycles in high yields. For 1-adamantyl isocyanate, a BNC5 heterocycle was obtained from the insertion of the C-N moiety into the five-membered borole, whereas for 4-methoxyphenyl isocyanate, a BOC5 heterocycle was generated from the insertion of the C-O unit. These reactions are believed to occur via a mechanism wherein coordination of the nucleophile to the borole (1-adamantyl, N-coordination or O-coordination for 4-methoxyphenyl) is followed by ring expansion to afford the observed seven-membered heterocycles. The selectivity to form B-O- or B-N-containing heterocycles is based on the polarization of the isocyanate implying tunable reactivity for the system. Having observed that isocyanates react as 1,2-dipoles with pentaphenylborole, we examined benzophenone and benzaldehyde, which both reacted to insert C-O units into the ring. This represents a new efficient method for preparing rare seven-membered boracycles.
五苯基硼烷与异氰酸酯、二苯甲酮和苯甲醛反应，高产率地生成了新的七元杂环。对于1-金刚烷基异氰酸酯，通过将C-N部分插入五元硼烷中得到了一个BNC5杂环，而对于4-甲氧基苯基异氰酸酯，通过插入C-O单元生成了一个BOC5杂环。据信这些反应是通过一种机制发生的，即亲核试剂与硼烷配位（1-金刚烷基，4-甲氧基苯基为N配位或O配位），随后进行环扩张，从而得到观察到的七元杂环。形成含B-O或B-N杂环的选择性基于异氰酸酯的极化，这意味着该体系具有可调节的反应活性。在观察到异氰酸酯与五苯基硼烷以1,2-偶极体的形式反应后，我们研究了二苯甲酮和苯甲醛，它们都发生反应将C-O单元插入环中。这代表了一种制备稀有七元硼杂环的新的有效方法。
