A series of recently prepared amine-alkylcyanoboranes (alkyl = i-Bu, sec-Bu, and benzyl; amine pyridine and quinuclidine) have been treated with Et,OBF, and then aqueous sodium hydroxide to form selected amine-alkyl(N-ethylcarbamoyl)boranes, which are some of the first reported analogues of the a-amino acids, leucine, isoleucine, and phenylalanine, respectively. Two intermediate nitrilium salts (sec-Bu and benzyl) have been fully characterized, demonstrating the unusual chemical stability of these boronium species. In addition, the full characterization of two amine-alkylcyanoboranes and one amine-alkyl(N-ethyl-carbamoy1)borane (R = i-Pr; valine analogues) are reported. 0020-1669/91/ 1330-1046%02.50/0 I , . ~ ~ ~, ~ 0 199 1 American Chemical Society Amine-Alkyl( N-ethylcarbamoyl) boranesBoron-I 1 NMR spectra were recorded at 115.8 MHz on the Nicolet 360 spectrometer in the solvents indicated; the spectrometer was not usually locked to the deuterium signal as signal drift was a couple of orders of magnitude lower than the broadening of the IlB signals. Chemical shifts are reported relative to Et20BF, as an external standard, with positive shift values being downfield. Coupling constants indicate 'H-I'B interactions, unless otherwise noted. Carbon-I3 NMR spectra were obtained in deuterated solvents by using the Bruker (1 25.76 MHz), Nicolet (90.8 MHz), or Varian XL-300 (75.4 MHz) spectrometers. Chemical shifts are reported in ppm downfield of tetramethylsilane, as established by comparison to the solvent chemical shifts: acetone-&, 206.0, 29.8; acetonitrile-d,, 118.2, 1.3; chloroform-d, 77.0; dichloromethane-d,, 53.8.Other Techniques. Infrared spectra were recorded in cm-' on a Perkin-Elmer 283 spectrophotometer as neat oils or KBr pellets and were referenced to polystyrene (1601.4 and 1583.1 cm-I). Intensities are reported in accordance with the Iiterature.l2 Melting points were obtained by using a Meltemp device in sealed, evacuated capillaries and are uncorrected. Mass spectra were determined on a Kratos MS-80 using the technique indicated. Elemental analyses were performed by Galbraith Microanalytical Labs, Knoxville, TN, or Desert Analytics, Tuscon, AZ.Experimental Procedures. Lithium Isopropyltrihydroborate. Isopropyllithium (361 mL X 0.52 M, 188 mmol) was reacted according to the modified' Noth" protocol with 1 equiv of dimethyl sulfide-borane (18.8 mL X 10.0 M, 188 mmol) over 2 h, cooled by a frozen acetonitrile slush (-50 "C), and allowed to warm to rmm temperature overnight. While the reaction solution was clear at low temperatures, a copious white precipitate appeared by morning. Boron-I 1 analysis revealed approximately by integration 73% Li-i-PrBH,, 17% LiBH4, and about 10% other products: "B NMR (THF) 8 -24.29 (q, J = 75.41 Hz).Lithium Isopropylcyanodihydroborate. Crude lithium isopropyltrihydroborate (==73% RBHC, estimated 137 mmol) was dissolved in 1 IO mL of THF and reacted with a deficiency of Hg(CN)2 (13.0 g, 51 mmol) at room temperature, added as a powder. The reaction was complete in 20 min, as...