A Mechanistic Alternative for the Intramolecular Hydroboration of Homoallylic Amine and Phosphine Borane Complexes

Abstract

Intramolecular hydroboration is demonstrated starting from homoallylic amine boranes upon activation by iodine. The process involves a B-iodoborane complex as the intermediate and may occur via internal displacement of iodide by the alkene to generate a cationic borane-alkene pi-complex on the way to hydroboration products. The reaction can be carried out using a catalytic amount of iodine.

Fundamental and Applied Properties of Borocations

“…The intermediacy of borenium cations (or their functional equivalents) in hydroboration was first considered by Vedejs and co-workers when studying the reactivity of (L)BH 2 X (X¼I or OTf, L¼amine or phosphine) [75][76][77]. Importantly, the hydroboration reactivity of the (L)BH 2 X species was distinct to that of the free borane, particularly in providing improved regioselectivity.…”

Magnesium Borohydride Confined in a Metal–Organic Framework: A Preorganized System for Facile Arene Hydroboration

“…The close CH⋅⋅⋅HB contacts observed in the experimental and calculated structures of 1 may also play an integral role, weakening the HB bond (as noted in aminoborane species) and facilitating BH 4 degradation 14. The proposed generation of BH 3 on heating 1 will be facilitated by release of a hydride as a good leaving group (stabilized by coordination to Mg, Figure 3), analogous to the mechanism elucidated for related intramolecular hydroboration reactions 31…”

Progresses on the Application of Stable Borane Adducts in the Synthesis of Organoborons

“…2003 年, Vedejs 等 [11] 以 I 2 为活化试剂(50 mol%)实现 了首例高烯丙基胺 1 的硼烷加合物分子内硼氢化反应, 生成的环状有机硼 2a 和 2b 经氧化得到相应的醇 3a 和 3b, 区域选择性主要受烯烃上的取代基 R 控制(Scheme 3). 该反应用催化量的 I 2 (10 mol%)同样可以顺利进行,…”