ISSN:
0947-3440
Keywords:
Silyl nitronates, trifluoromethyl-substituted, NMR studies of
;
Nitroalkanes, fluorinated, α,α-doubly deprotonated
;
Nitroaldol additions, diastereoselective
;
[3 + 2] Cycloadditions
;
Isoxazolidines, trifluoromethyl-substituted, conformational studies of
;
Aminoethanols and -propanols, trifluoromethyl-substituted, X-ray studies of
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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).
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.1995199507162
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