Addition compounds of alkali metal hydrides. 27. A general method for preparation of the potassium 9-alkoxy-9-boratabicyclo[3.3.1]nonanes. A new class of stereoselective reducing agents

Abstract

The reaction in tetrahydrofuran of potassium hydride with representative B-alkoxy-9-borabicyclo[3.3.1]nonanes (B-OR-9-BBN) containing alkoxy groups with increasing steric requirements was examined in detail to establish the generality of this synthesis of the corresponding potassium 9-alkoxy-9-boratabicyclo[3.3.1]nonanes (K9-OR-9-BBNH) and the stereoselectivities of these new reagents for the reduction of cyclic ketones. For R = Me and n-Bu, the reactions with potassium hydride are very fast, almost instantaneous, even at 0 °C. However, the products are unstable and rapidly undergo redistribution, even in the presence of excess potassium hydride. Moderately hindered alkoxy derivatives, R = 2-Pr and 2-Bu, react somewhat slower (1 h at 0 °C and 25 °C, respectively) and the products are stable to redistribution. More hindered alkoxy derivatives, R = t-Bu, t-Am, Thx, require 24 h at 25 °C. Even more hindered alkoxy groups, R = 3-ethyl-3-pentyl and 2,4-dimethyl-2-pentyl, require even longer reaction times and higher temperatures. All reagents show high stereoselectivities in the reduction of cyclic ketones, with the stereoselectivities generally increasing with increasing steric requirements of the alkoxy substituent. The thexyl derivative appears especially favorable, with the byproducts of the reaction readily removed from the reaction mixture.

Synthesis, Reactions, and Structures of Heterocycle-Tethered Boranes and Their Precursors

“…Petroleum ether (bp 40–60 °C) and other solvents were distilled under N 2 atmosphere according to the standard procedures. 9-Methoxy-9-BBN was synthesized from 9-BBN by the literature procedure . Other chemicals were obtained from commercial sources and used as received.…”

“…9-Methoxy-9-BBN was synthesized from 9-BBN by the literature procedure. 36 Other chemicals were obtained from commercial sources and used as received. 1 H (400 MHz), 13 C (102.6 MHz), 19 F (376.5 MHz), and 11 B (128.3 MHz) NMR spectra were recorded at room temperature.…”

Chiral recognition in aqueous solution. Search for water-soluble chiral hosts with apolar binding sites

“…15: mp 77 °C (ether); NMR (500 MHz, CDC13) 1.1-1.2 (m, 4 H, OCH2CH2CH2), 1.35-1.6 (m, 8 H, OCH2CH2CH2CH2), 2.07 (s, 12 H, (C/f3)2NCH2), 2.14 (s, 12 H, aryl-CH3), 2.24 (s, 3 H, NCH3), 2.2-2.4 (m, 4 H, NCH2CH2C), 2. 4-2.6 (m, 4 H, NCH2CH2C), 2.93 and 2.95 (AB, J = 14.5 Hz, 4 H, N-CH2-aryl), 3.55-3.75 (m, 8 H, 0CH2CH2CH2CH2CH20), 6.47 (d, J = 8.0 Hz, 2 H, Bp-3,3'-H), 6.82 (s, 4 H, aryl-HDPM), 4 H,4',5,; MS, m/z (70 eV) (relative intensity) 775 (14, M+), 70 (100); m/z (16 eV) NMR (500 MHz, CDC13) 1.1-1.2 (m, 4 H, OCH2CH2CH2), 1. 4-1.6 (m, 8 H, OCH2Ctf2CH2CH2), 2.17 (s, 12 H, aryl-CH3), 2.24 (s, 3 H, NCH3), 2.30 (s, 3 H, NCH3), 2.S-2.6 (m, 8 H, NCH2CH2C), 3.02 and 3.36 (AX, J = 12.2 Hz, 4 H, MeN-CH2-Aryl), 3.55-3.8 (m, 8 H, 0CH2CH2CH2CH2Ctf20), 6.46 (d, J = 8.2 Hz, 2 H, DBA-2,10-H),43 6.85 (d, J = 7.3 Hz, 2 H, DBA-4,8-H), 6.90 (s, 4 H, aryl-HDPM), 7.09 (t, J =* 7.8 Hz, 2 H, DBA-3,9-H); MS, m/z (relative intensity) JV,lV,JV ',JV,.…”

“…(4) Lehn, J. M. Science (Washington, D.C.) 1985, 227, 849-856. (5) Jolley, S. T.; Bradshaw, J. S.; Izatt, R. M. J. Heterocycl. Chem.…”

Copper-Catalyzed γ-Selective Allyl−Alkyl Coupling between Allylic Phosphates and Alkylboranes

“…Specifically, a THF solution of alkylborane 2a was prepared via hydroboration of styrene ( 1a ) with 9-borabicyclo[3.3.1]nonane (9-BBN-H) dimer ( 1a /B 1.2:1) at 60 °C (Scheme ). Subsequently, the THF solution of 2a (0.75 mmol) was treated with t -BuOK (0.5 mmol, 1 M in THF) at rt for 5 min to yield an alkylborate, to which CuOAc (10 mol %) was added . Allylic phosphate 3a (0.5 mmol) was then added to the mixture, which was heated at 60 °C for 8 h to afford allyl−alkyl coupling product ( E )- 4aa in 80% isolated yield (based on 3a ; 89% convn of 3a ) .…”