Mechanistic Studies on the O-Directed Free-Radical Hydrostannation of Disubstituted Acetylenes with Ph3SnH and Et3B and on the Iodination of Allylically Oxygenated α-Triphenylstannylalkenes
摘要:
The free-radical hydrostannation of 1 with Ph3SnH and catalytic Et3B in PhMe has been mechanistically probed. At high Ph3SnH concentrations, the O-directed hydrostannation pathway dominates, and 2 is formed with good selectivity (ca. 11.1:1). Substantially lower stannane/substrate concentrations increase the amount of tandem 5-exo-trig cyclization product 3 that is observed.
The stannylvinyl cation that never was! New concentration- and temperature-dependent probe studies confirm an entirely free radical mechanism and O–Sn coordinative control of the hydrostannation of propargylically-oxygenated dialkyl acetylenes with stannanes and cat. Et3B
作者:Hamish A. Watson、Soraya Manaviazar、Hannah G. Steeds、Karl J. Hale
DOI:10.1016/j.tet.2020.131061
日期:2020.5
β-scission. A second alkynol probe 23 was also studied in this O-directed freeradical hydrostannation process. It gave rise to an α:β stannyl radical addition regiochemistry that changed markedly in favor of the α-adduct (26) when the reaction was conducted at high stannane concentrations. This outcome confirmed that O–Sn coordinative control must be responsible for the strong α-regiochemical preference
β-环丙基炔丙醇57与锡烷和Cat的O定向自由基氢化。在THF / H 2 O或PhMe / MeOH中的Et 3 B未能传递任何预期的α-锡烷基乙烯基阳离子捕获产物。取而代之的是,仅检测到α-锡烷基-β-环丙基乙烯基自由基中间体,这些中间体由于消除了β断裂而经历了快速的H原子提取和/或环丙烷开环。在该O取向的自由基氢化过程中还研究了第二炔醇探针23。它引起了α:β苯乙烯基自由基加成区域化学反应,显着改变,有利于α加合物(26当在高锡烷浓度下进行反应时。这一结果证实,O-Sn协调控制必须对锡烷浓度较高时运行的锡烷基锡的强烈α-区域化学偏好负责,因为非协调,电子控制的苯乙烯基自由基的添加总是会产生固定且相同的比率α:β-区域异构体的组成。27的形成进一步证实了这些反应的完全自由基性质。
Mechanistic Studies on the <i>O</i>-Directed Free-Radical Hydrostannation of Disubstituted Acetylenes with Ph<sub>3</sub>SnH and Et<sub>3</sub>B and on the Iodination of Allylically Oxygenated α-Triphenylstannylalkenes
作者:Paschalis Dimopoulos、Jonathan George、Derek A. Tocher、Soraya Manaviazar、Karl J. Hale
DOI:10.1021/ol051937d
日期:2005.11.1
The free-radical hydrostannation of 1 with Ph3SnH and catalytic Et3B in PhMe has been mechanistically probed. At high Ph3SnH concentrations, the O-directed hydrostannation pathway dominates, and 2 is formed with good selectivity (ca. 11.1:1). Substantially lower stannane/substrate concentrations increase the amount of tandem 5-exo-trig cyclization product 3 that is observed.