Silyl nitronates of 2,2,2-trifluoronitroethane and of 1,1,1-trifluoro-2-nitropropane [SiMe3, SiMe2(tBu), SiMe2CMe2-CHME2] were prepared and their reactions studied. – The TBDMS nitronate of the nitroethane is present at the (E) and (Z) isomer (2.3:1 at room temperature; EA = 9.3 kcal mol−1 for their isomerization). BU4NF-catalyzed silyl nitro aldol additions to aldehydes show reasonable selectivities for the formation of the syn diastereoisomers of 5–13 (a. 4:1; with the non-fluorinated analogs anti isomers prevailing!). The anti epimers (5–9, 12, 13, 17–20) in the trifluoromethyl series can be prepared by diastereoselective protonation of the corresponding O-silyl lithium nitronates (ca. 9:1, Scheme 3). Careful reduction of the NO2 groups (H2/Raney nickel) gives trifluoroamino alcohol derivatives (22–30, Scheme 4). –The trimethylsilyl nitronates are also used for 1,3-dipolar cycloadditions (to 1-hexene, styrene, methyl vinyl ketone, and acrylates) to give N-(silyloxy)isoxazolidines (2–40; Scheme 5). The configuration of the major products (2,3-cis, 3,5-trans) was derived from NMR measurements, X-ray structure determinations, and thermal equilibration studies. The major course of reactions was thus derived to be an exo approach of the dipolarophiles to the (Z)-silyl nitronates (Scheme 8).– Some conversions of the N-(silyloxy)isoxazolidines (treatment with acid, base, and Raney nickel) are also described (products 42–51).

Preparation and reactions of silyl nitronates derived from 2,2,2‐trifluoronitroethane. Diastereoselective synthesis of trifluoromethyl‐substituted aminoethanols and ‐propanols

A general approach to the synthesis of borohydride complexes containing one or two dinitroamide fragments has been suggested. Based on a smooth substitution of halide in haloborane or dibromoborane complexes with N,N-dinitroamide salts, this method provides various N,N-dinitroamidoboranes complexes in good yields and in analytically pure form. By means of spectroscopic and computational methods, it was demonstrated that dinitroamidoborane complexes could form as both B,N- and B,O-isomers, which did not interconvert at ambient temperature.

Synthesis and Structure of N,N-Dinitroamidoborane Complexes.

Basic biogeogenetic concepts are outlined regarding the structural elements in the high-molecular organic material of sapropelites and their transformations on hydrothermal pyrolysis during high-temperature alkaline hydrolysis. The applicability of these concepts to the identification of the molecular structure of such organic material and the assessment of its reactivity is demonstrated.

Biogeogenetic concepts regarding the organic structure of sapropelites

The DNMR method was used to study the 1,3-(O,O) migration of the heteroorganic fragment in the diethylboron and trimethylsilyl esters of bis(carbomethoxymethane)nitronic acid, and it was shown that the migration is accomplished via a multicenter cyclic transition state.

Mechanism for exchange of heterooeganic fragment between oxygen atoms of -O-N-O group in nitronic acid esters

1.

Direct measurements have, for the first time, been carried on dienone-2H-pyran isomerization in 1,1-dicarbonyl 1,3-dienes.




2.

A study has been made of the effect of solvent and substituents on the position of the point of equilibrium in such systems; thermodynamic and activation parameters have been determined for the isomerization process, and the effect of the solvent on these parameters have been studied.




3.

Reducing the efficiency of conjugation and increasing the steric strain in the dienone shifts the points of dienone-2H-pyran equilibrium to the pyran side. An increase in the dipole moment of the solvent has the opposite effect.




4.

The solvent has little effect on rate constant values for the dienone-2H-pyran isomerization.

K. M. Litvak

Papers

Mechanism for exchange of heterooeganic fragment between oxygen atoms of -O-N-O group in nitronic acid esters

A direct PMR study of dienone-2h-pyran valence isomerization in 1,1-dicarbonyl 1,3-dienes