Synthesis, Properties, and Crystal Structure of Silyl Nitronates (Silyl Esters of aci‐Nitroalkanes): Towards the S_N2 Reaction Path with Retention of Configuration at Silicon

Abstract

An efficient and flexible method for the preparation of silyl nitronates is described (see 1–10). NMR. spectral investigations indicate a rapid 1,3‐silyl migration process, with an activation energy of about 10 kcal mol−1. X‐ray crystallographic studies on the silyl nitronates 3 and 8 show structures that lean towards an SN2 retention pathway at silicon.

1,4‐Diazabicyclo[2.2.2]octane (DABCO) as an Efficient Reagent for the Synthesis of Isoxazole Derivatives from Primary Nitro Compounds and Dipolarophiles: The Role of the Base

“…[2] One synthetic protocol is based on the conversion of the nitro compounds into alkyl [3] or silyl nitronates, [4][5][6] which is then followed by cycloaddition and elimination. Other methods require the treatment of the nitro compounds with acylating agents, or the reagents must be heated in the presence of strong acids.…”

Five‐Membered Cyclic Nitronates in C–C Coupling with 1‐(tert‐Butyldimethylsilyloxy)‐1‐methoxyethylene

“…[7] Thus, to determine the structures of the isoxazolidines 5 the relative configurations of the three stereocentres, namely the N, C-3 and C-5 atoms, had to be identified. From the literature data, [8] an envelope conformation with the nitrogen atom in the envelope flap and the OTBS substituent in a pseudo-axial position was assumed for the isoxazolidines 5. The NOESY technique was used to determine the arrangement of the substituents.…”

Improved Nitroaldol Reactions and Reductive Routes to Vicinal Aminoalcohols

“…-To a solution of 5.4 mmol lithium diisopropylamide in 15 ml T H F stirred at -78" under Ar were added 0.84 g (5.0 mmol) @-methoxyphenyl)nitromethane6), and after 30 min 0.90 g (6.0 mmol) (1-buty1)dimethylsilyl chloride, dissolved in 2 ml THF. The temperature was allowed lo rise to +20" overnight, the solvent removed in vacuo, and the residue triturated with 25 ml pentane, filtered through Celite and concentrated (cJ [12]). The 0.61 g (43.6%) of crude silyl nitronate thus obtained were recrystallized from pentane to furnish crystals suitable for X-ray structure analysis (Fig.…”

“…spectra were recorded with a Varian EM 390 spectrometer, chemical shifts are given in ppm, coupling constants in Hz. The silyl nitronates were prepared as previously described by us [12]; for large scale preparations see also footnote 5.…”