Reaction of aminosulfur trifluorides with alcohols: inversion vs. retention

Synthesis and in vitro evaluation of the antitumor potential and chemo-sensitizing activity of fluorinated ecdysteroid derivatives

“…due to a rigid steroid skeleton, as in our case) prevent an S N 2 attack. 16 Altogether, compound 5 was identified as 14-deoxy-14,25-difluoroponasterone A 2,3;20,22-diacetonide, a new ecdysteroid.…”

“…Based on these, it could be evidenced that compounds 3-5 contain a fluorine atom connected to the C-25, and that compound 5 contains another fluorine substituent also at position C-14. Fluorination of alcohols catalyzed by DAST can take place through either S N 1 or S N 2 reaction mechanism, which also determines the stereo-specificity of the reaction: 16 a priori, the 14-F substituent in compound 5 can be present in either α or β position. The latter case would also involve a change of the initially trans C/D ring junction to cis.…”

Introduction of Fluorine and Fluorine‐Containing Functional Groups

“…133 The mechanism of DAST‐mediated fluorination is proposed to begin with nucleophilic attack of the alcohol substrate on the sulfur atom of DAST to form an alkoxyaminodifluorosulfane intermediate134 that is activated for S N 2 attack by fluoride. In some cases, however, the fluorination with DAST affords products consistent with an S N 1 mechanism 133h. Additional drawbacks of DAST include moisture sensitivity as well as a propensity to explode upon heating 107e…”

Synthesis of optically active vicinal fluorocyclopentanols and fluorocyclopentanamines by enzymatic deracemization

“…Optically active organofluorine compounds were obtained by such methods as yeast reduction of fluorinated ketones, hydrogenation of activated olefinic double bonds, and deracemization or desymmetrization of fluorinated compounds. [2][3][4][5] Vicinal halocyclopentanols are synthetic blocks for a number of chiral natural and synthetic products. These compounds are used to prepare various biologically active compounds, in particular, prostaglandins and precursors of leukotrienes.…”

“…[6][7][8][9][10] We have previously synthesized all possible stereoisomers of cis-halocyclohexanols (Hlg = I, Br, Cl, F) using the kinetic enzymatic resolution of corresponding racemates (Scheme 1). Haufe et al 3 and Hashimoto et al 4 described the enzymatic deracemization of trans-2-fluorocyclohexane-1-ols, 2-fluorocycloheptan-1-ols, and 2fluorocyclooctan-1-ols using Pseudomonas Fluorescence lipase. Scheme 1.…”