Tetrahedron p. 2021 - 2028 (1987)
Update date:2022-08-16
Topics:
Kauffmann, Thomas
Abel, Thomas
Schreer, Martin
Wingbermuehle, Dorothea
The reagent Cl3TiMe in diethylether methylates heptanal (2) as well as 2-hexanone (5) and the ethyl ester of 4-oxo-valeric acid (4) to afford in high yields 2-octanol (2a), 2-hydroxy-2-methylhexane (5a), and the ethyl ester of 4-hy-droxy-4-methylvaleric acid (4a), respectively. Addition of a small amount of tetrahydrofuran to the solution does not affect the methylation of heptanal, whereas methylation of the ketones 4 and 5 is depressed heavily. These observations and IR spectroscopic data lead to the hypothesis, that shielding of the reagent by coordinating solvent molecules is the main reason for aldehyde selectivity of Lewis acidic reagents such as Cl3TiMe, Cl2CrMe, or ClMo(O)=CH2 in electron donor solvents. The reactivity of Cl3TiMe towards heptanal in CH2Cl2 is clearly hampered by a small amount of either 1,2-dimethoxyethane, dioxane, pyridine, 2,2-dipyridyl, or diphos . The reactivity of Cl4NbMe towards heptanal is reduced even by tetrahydrofuran.
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