Borane-Catalyzed Stereoselective C–H Insertion, Cyclopropanation, and Ring-Opening Reactions

Abstract

This work demonstrates the highly selective metal-free catalytic reactions of a-aryl a-diazoesters with a range of (hetero)cycles and olefins using Lewis acidic boranes. The simple, mild reaction protocol employed represents an alternative to the commonly used precious metal systems and may provide future applications in the generation of biologically active compounds.

Borane catalysed cyclopropenation of arylacetylenes

“…However, multinuclear spectroscopic data of the isolated compound confirmed the formation of methyl 3-oxo-2,3diphenylpropanoate (see ESI) formed from the homologation of benzaldehyde with the diazo compound (Roskamp-Feng reaction). 21 We propose the mechanism of the cyclopropenation reaction to proceed in a similar manner to that for the cyclopropanation reaction reported in our previous studies 12 (Figure 2). Initially, the Lewis acidic B(C6F5)3 binds effectively with the ester functionality of the α-aryl α-diazoester 1.…”

“…Carbene transfer reactions are one of the most fundamental reactions in organic synthesis and widespread studies have been conducted to explore the synthetic utility of carbenes for making a variety of novel compounds. 11 Recently, we 12 and Wilkerson-Hill 13 observed that catalytic amounts of B(C6F5)3 enable the cyclopropanation reactions of styrenes (Scheme 1A) using α-aryl α-diazoesters. This exciting outcome motivated us to investigate this reactivity further to see if arylacetylenes could also be used as substrates in reactions with α-aryl αdiazoesters using B(C6F5)3 as a catalyst.…”

Tris(pentafluorphenyl)boran‐katalysierte Erzeugung von Carbenium‐Ionen und autokatalytische Pyrazol‐Synthese – eine theoretische und experimentelle Studie

“…Kürzlich haben wir [5] und andere [6a] die katalytische Aktivität von B(C 6 F 5 ) 3 bei der Aktivierung von Diazoestern untersucht, die zur Bildung von Carben‐Zwischenprodukten durch die Abspaltung von N 2 führt. Die Carben‐Zwischenprodukte können anschließend als Bausteine für die Synthese neuartiger organischer Moleküle durch eine Reihe verschiedener Reaktionen wie O‐H/N‐H/C‐H‐Insertion, [5a, 6b,d,g,h] Azid/Carbonat‐Transfer, [6e,f] Cyclopropanierung/Cyclopropenierung [5a, 6c] und für die Ringöffnung heterocyclischer Verbindungen verwendet werden [5a] . In dieser Studie interessierten wir uns für die B(C 6 F 5 ) 3 ‐katalysierte Synthese von Pyrazolen aus Vinyldiazoacetaten, bei der die N 2 ‐Funktionalität des Diazo‐Ausgangsmaterials nicht freigesetzt wird.…”

The synthesis, properties, and reactivity of Lewis acidic aminoboranes

“…We began by evaluating amines that could provide a comprehensive scope of both steric and electronic properties. As noted above, we previously reported the synthesis of the phenothiazyl aminoborane (1) and we further synthesized aminoboranes containing phenoxazine (2), diphenylamine (3), 20 trimethylsilyl (4), 21 carbazole (5), and acridane ( 6) motifs (Figure 2). These amines provide a platform to understand the impact that fused ring systems have on the Lewis acidity.…”

“…Tri-coordinate boranes have found diverse applications as Lewis acidic reagents for stoichiometric and catalytic transformations. [1][2][3][4] The advent of frustrated Lewis pair (FLP) chemistry has brought the synthesis of novel Lewis acidic boranes into the spotlight. [5][6][7] The steric and electronic properties of tri-coordinate boranes can easily be modified through simple organometallic transformations, opening up a substantial library of available Lewis acids.…”