Categories: O-H Bond Formation >
Cleavage of carbonates
Different from most carbonates the allyloxy carbonyl protecting group can be cleaved under neutral conditions using expensive precious metals catalysts. Two new Fe-catalyzed protocols enable a mild liberation of alcohols from allylcarbonates, broad functional group tolerance, and exclusive chemoselectivity.
A. P. Dieskau, B. Plietker, Org. Lett., 2011, 13, 5544-5547.
Carbon tetrabromide catalyzes O-tert-butoxycarbonylation of functionalized phenols without any side reactions (bromination, addition of CBr3 to a double bond, and formation of symmetrical diaryl carbonates, cyclic carbonates, or carbonic-carbonic anhydrides). The parent phenols are regenerated from the O-t-Boc derivatives by the catalyst system CBr4-PPh3 without affecting other functional groups.
S. V. Chankeshwara, R. Chebolu, A. K. Chakraborti, J. Org. Chem., 2008, 73, 8615-8618.
The reaction of chiral 1-aminoalkylepoxides with CO2, generated from acidic treatment of an aqueous solution of NaHCO3 at room temperature, efficiently afforded enantiopure cyclic carbonates with total selectivity. Carbonates were readily transformed into the corresponding diols by reaction with LiAlH4 or by basic hydrolysis.
J. M. Concellón, V. del Solar, S. Carcía-Granda, M. R. Díaz, J. Org. Chem., 2007, 72, 7567-7568.
An efficient one-pot procedure for the zinc-mediated reduction of nitroarenes in the presence of chloroformates leads to the corresponding N,O-bisprotected hydroxylamines in good yield under ambient conditions in THF-water mixtures. Solvolysis of the bisprotected hydroxylamines with sodium methoxide at room temperature provides access to synthetically versatile N-aryl-N-hydroxy carbamates in excellent yields.
A. Porzelle, M. D. Woodrow, N. C. O. Tomkinson, Synlett, 2009, 798-802.