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A diastereoselective approach to (2 R ,5 S )- and (2 S ,5 S )-2-methyl-1,6-dioxaspiro[4.5]decane 1 and 1a is described. The route starts with an alkylation reaction among the cyclopentanone N , N -dimethylhydrazone 6 and the chiral iodides ( R )- 3 or ( S )- 3 , derived from the enantiomers of ethyl β-hydroxybutyrate, controlling the estereocenter at C-2 of the molecules. The alkylated products 7 and 7a were easily transformed into the 1,8- O -TBS-1,8-dihydroxy-5-nonanones 9 and 9a in four steps, and a subsequent stereoselective spiroketalization, in acidic media, afforded a Z : E mixture (1:2) of compounds 1 and 1a . |
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