We report the first syntheses—from commercially available 3-chloro-2-fluoroprop-1-ene (
9)—of key garlic-derived compounds containing sp
2-fluorine. We also report synthesis of fluoro-5,6-dihydrothiopyrans by trapping 2-fluorothioacrolein (
15). Thus, difluoroallicin (
12,
S-(2-fluoro-2-propenyl) 2-fluoroprop-2-ene-1-sulfinothioate) is prepared by peracid oxidation
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We report the first syntheses—from commercially available 3-chloro-2-fluoroprop-1-ene (
9)—of key garlic-derived compounds containing sp
2-fluorine. We also report synthesis of fluoro-5,6-dihydrothiopyrans by trapping 2-fluorothioacrolein (
15). Thus, difluoroallicin (
12,
S-(2-fluoro-2-propenyl) 2-fluoroprop-2-ene-1-sulfinothioate) is prepared by peracid oxidation of 1,2-bis(2-fluoro-2-propenyl)disulfane (
11).
S-2-Fluoro-2-propenyl-
l-cysteine (2-fluorodeoxyalliin,
13), synthesized from cysteine and characterized by X-ray crystallography, is oxidized to its
S-oxide, 2-fluoroalliin (
22). The latter, with alliinase-containing powdered fresh garlic, gives a mixture of
12, allicin (
1), and isomers of monofluoroallicin (
23), indicating that
22 serves as a substrate for garlic alliinase. Upon heating,
12 generates transient
15, which dimerizes giving difluoro vinyl dithiins
6 and
7. Ethyl acrylate trapping of
15 affords 5- and 6-substituted 3-fluoro-5,6-dihydro-4
H-thiopyrans (
19 and
20). In 1,1,1,3,3,3-hexafluoro-2-propanol (HEFP) as solvent,
12 is converted into trifluoroajoene ((
E,
Z)-1-(2-fluoro-3-((2-fluoro-2-propenyl)sulfinyl)prop-1-en-1-yl)-2-(2-fluoro-2-propenyl)disulfane;
18). Liquid sulfur converts
11 to a (CH
2=CFCH
2)
2S
n mixture (n = 4–15), characterized by UPLC-(Ag
+)-coordination ion spray-mass spectrometry.
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