2-fluoro-1-tetralone

Asymmetric fluorination of the lithium enolate derived from tetralone 307 has been achieved with several new chiral A-fluoro-l,2-benzothiazine reagents (Scheme 44) <2000JOC7583, 2000CPB1954, see also 1999JFC(97)65>. For instance, sulfonamides 149 and 150 afford the opposite enantiomers of fluoroketone 308 in up to 79% yield and 62-70% ee. 

Access to optically active 2-fluoro-l-tetralone 53 was achieved using the same palladium-mediated cascade reaction [30]. The catalytic enantioseiective decarbox-ylative protonation of 2-fluoro benzyl P-keto ester 54 in the presence of 30 mol% of quinine 20 afforded enantioenriched (S)-tetralone 53 in 65% ee (Scheme 7.24). The reaction was very sensitive to the nature of the palladium catalyst used. Furthermore, a minor amount of defluorinated product was observed. Several other cinchona derivatives were tested including analogues of cinchonine described by Brunner in organocatalytic EDP (see Section 7.5.3), but these chiral inductors afforded low selectivities (<30% ee). 

The combination of boron trifluoride etherate and tert-butyl nitrite,17 in place of the conventional conditions (NaNC>2, HC1, HBF4), followed by decomposition of the diazonium salt in chlorobenzene afforded 5-fluorobenzo[c]phenanthrene (ll).l7b Nitrosonium tetrafluoroborate has been used to diazotize 8-amino-1-tetralone (12) en route to 8-fluoro- 1-tetralone (13).18... 

As shown in Scheme 12.67, the process for producing the compound 265, (a useful intermediate for production of camptothecin derivatives) involves the hydrogenation of 5-acetamido-7-fluoro-8-methyl-l-tetralone 270, to 5-acetamido-7-fluoro-8-... 

The Behenna-Stoltz protocol was soon applied to a-fluoroketones. As shown in Scheme 5.26, the silyl enol ethers 80 of 2-fluoro-indanone, tetralone-, and ben-zosuberone can be reacted with allyl or methallyl carbonate to give the tertiary a-fluorinated ketones 81 in 83-95% ee [43]. The procedure that was also applied to an allylation of 4,4-dimethyl-6-fluorocyclohexenone offers an alternative to the enantioselective fluorination of enolates on the one hand and the decarboxylative allylation of fluorinated P-keto esters on the other hand vide infra). 

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