Biphilic Organophosphorus-Catalyzed Intramolecular C(sp(2))-H Amination: Evidence for a Nitrenoid in Catalytic Cadogan Cyclizations.
Biphilic Organophosphorus-Catalyzed Intramolecular C(sp(2))-H Amination: Evidence for a Nitrenoid in Catalytic Cadogan Cyclizations.
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DOI：
10.1021/jacs.7b13803
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发表时间：
2018-02-28
影响因子：
15
通讯作者：
Radosevich AT
中科院分区：
文献类型：
--
作者：
Nykaza TV;Ramirez A;Harrison TS;Luzung MR;Radosevich AT
小环磷酸环烷（1,2,2,3,4,4-六甲基磷酸烷，3）在氢硅烷末端还原剂存在下催化分子内C-N键形成邻硝基和苯乙烯基衍生物的杂环化。该方法在操作简单的均相有机催化条件下可扩展地获得多种咔唑和吲哚化合物，如在1克尺度上进行的17个例子所证明的那样。原位核磁共振反应监测研究支持催化PIII/PV=O循环的机制，其中三配位磷化合物3代表催化静息状态。对于邻硝基联苯催化转化为咔唑，确定了磷烷催化剂3（一级）、底物（一级）和苯硅烷（零级）的动力学反应顺序。对于差5取代的2-硝基联苯，吸电子取代基加速了转化（Hammett factor ρ = +1.5），这与在速率决定步骤中硝基底物上负电荷的累积一致。限制转换率的脱氧事件的DFT模型暗示了在磷酸烷催化剂3和2-硝基联苯底物之间的速率决定（3+1）电加成，形成未观察到的五配位螺旋-双环二恶氮膦烷，其通过（2+2）环还原分解，得到一个等效的磷酸烷p -氧化物3•[O]和2-亚硝基联苯。对C-N键形成事件的实验和计算研究表明，在3和2-亚硝基联苯之间有一个恶氮磷（2+1）加合物参与，通过磷烷p -氧化物3•[O]的损失，通过C-H以类似硝基烯的方式插入，得到所观察到的咔唑产物。
A small-ring phosphacycloalkane (1,2,2,3,4,4-hexamethylphosphetane, 3) catalyzes intramolecular C–N bond forming heterocyclization of o-nitrobiaryl and –styrenyl derivatives in the presence of a hydrosilane terminal reductant. The method provides scalable access to diverse carbazole and indole compounds under operationally trivial homogeneous organocatalytic conditions, as demonstrated by 17 examples conducted on one-gram scale. In situ NMR reaction monitoring studies support a mechanism involving catalytic PIII/PV=O cycling, where tricoordinate phosphorus compound 3 represents the catalytic resting state. For the catalytic con-version of o-nitrobiphenyl to carbazole, the kinetic reaction order was determined for phosphetane catalyst 3 (first order), substrate (first order), and phenylsilane (zeroth order). For differentially 5-substituted 2-nitrobiphenyls, the transformation is accelerated by electron–withdrawing substituents (Hammett factor ρ = +1.5), consistent with the accrual of negative charge on the nitro substrate in the rate-determining step. DFT modeling of the turnover-limiting deoxygenation event implicates a rate-determining (3+1) cheletropic addition between the phosphetane catalyst 3 and 2-nitrobiphenyl substrate to form an unobserved pentacoordinate spiro-bicyclic dioxazaphosphetane, which decomposes via (2+2) cycloreversion giving one equivalent of phosphetane P-oxide 3•[O] and 2-nitrosobiphenyl. Experimental and computational investigations into the C–N bond forming event suggest the involvement of an oxazaphosphirane (2+1) adduct between 3 and 2-nitrosobiphenyl, which evolves through loss of phosphetane P-oxide 3•[O] to give the observed carbazole product via C–H insertion in a nitrene-like fashion.
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影响因子：
2.1
作者：
Davies, IW;Smitrovich, JH;Bazaral, C
通讯作者：
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影响因子：
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影响因子：
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