Selective hydroboration of alkenes and alkynes in the presence of aldehydes and ketones

Abstract

The reactions of terminal alkenes in the presence of ketones or aldehydes with a variety of borane reagents have been investigated. It was found that the selective hydroboration of a terminal alkene in the presence of a ketone or an aldehyde is most efficient when dicyclohexylborane is used as the hydroborating agent. The hydroboration of olefinic ketones and olefinic aldehydes with dicyclohexylborane generates the corresponding hydroxyaldehydes and hydroxyketones in good yields after oxidation with sodium perborate. The hydroboration of alkynyl ketones and alkynyl aldehydes with dicyclohexylborane yields the corresponding olefinic carbonyl compounds after protonation, or dicarbonyl compounds after oxidation.Key words: hydroboration, reduction, dicyclohexylborane, hydroxyaldehyde, hydroxyketone.

4,4,5,5‐Tetraphenyl‐1,3,2‐dioxaborolane: A Bulky Borane for the Transition Metal Catalysed Hydroboration of Alkenes

“…Similar selectivities have been reported in an elegant study by Kabalka et al for reactions using HBCy 2 . [11] Figure 2. Novel organoboronates generated from the catalysed hydroboration of alkenes with 3.…”

“…IR (nujol): ν = 3057, 2943, 2877, 1716(C-O), 1597, 1493, 1446, 1381, 1321, 1263, 1173, 1034 2897,2854,1599,1479,1464,1433,1379,1215,1149,1095,1026,999,958,908,883,789,748,692,634 with Paratone-N oil, mounted using a glass fibre and frozen in the cold stream of the goniometer. A hemisphere of data was collected with a Bruker AXS P4/SMART 1000 diffractometer using ω-and θ-scans with a scan width of 0.3°and exposure times of 10 (7) and 40 s (11). The detector distances were 5 cm.…”

“…[16b] The structures were solved by direct methods (7) or Patterson methods (11) and refined by full-matrix least squares on F 2 .…”

Capturing HBCy2: Using N,O‐Chelated Complexes of Rhodium(I) and Iridium(I) for Chemoselective Hydroboration

“…Amongst hindered boron hydride sources,H BCy 2 has been shown to serve as ac hemoselective reagent for the hydroboration of alkenes in the presence of an aldehyde or ketone. [8] We were particularly interested in exploring the hydroboration reactivity of HBCy 2 whilst bonded to al atetransition-metal center,w ith the possibility of eliciting achange in hydroboration chemoselectivity as aconsequence of metal-ligand cooperation. [9] More importantly,asawhole, this study highlights the potential inclination of 1,3-LXtype [10] ligands,f or example,a midates,a midinates,g uanidinates,c arboxylates,a nd triflates,t oc ooperate in EÀH functionalization with alate transition metal.…”

Systematic Variation of Cyanobuta‐1,3‐dienes and Expanded Tetracyanoquinodimethane Analogues as Electron Acceptors in Photoactive, Rigid Porphyrin Conjugates

“…[22] After protection of the ketone functionality as dioxolane (Ϯ)-40, hydroboration of the alkene with Cy 2 BH·THF [attempts with 9-borabicyclo[3.3.1]nonane (9-BBN-H), failed] and subsequent oxidation resulted in the formation of primary alcohol (Ϯ)-41. [23] By means of Gabriel synthesis, transformation into phthalimide (Ϯ)-42 by a Mitsunobu reaction, and subsequent cleavage with hydrazine led to primary amine (Ϯ)-43. Cyclization to imine (Ϯ)-44 occurred upon deprotection of the dioxolane group with HCl.…”