Sodiumhypochlorite pentahydrate (NaOCl·5H2O) can be used toward the efficient glycol cleavage of trans-cyclic glycols, which are generally resistant to this transformation. Interestingly, the reaction of cis-cyclic glycols with NaOCl·5H2O is slower than that observed for the corresponding trans-isomer. This trans selectivity is in sharp contrast to traditional oxidants used for glycol cleavage. Acyclic
Selectivity in Lewis acid-mediated fragmentations of peroxides and ozonides: application to the synthesis of alkenes, homoallyl ethers, and 1,2-dioxolanes †
作者:Patrick H. Dussault、Hyung-Jae Lee、Xuejun Liu
DOI:10.1039/b001391i
日期:——
Fragmentation of dialkyl peroxides and ozonides is strongly influenced by the choice of Lewis acid. TiCl4 promotes C–O ionization (SN1 reaction) of tertiary peroxides while SnCl4 and BF3·OEt2 promote O–O heterolysis (Hock reaction). The cationic intermediates are trapped with allyltrimethylsilane to afford allylated alkanes and homoallyl ethers. In the absence of a nucleophile, ozonides (1,2,4-trioxolanes) invariably undergo O–O heterolysis. However, the combination of allyltrimethylsilane and SnCl4 results in formation of 1,2-dioxolanes via trapping of intermediates derived from SN1 ionization.
Catalytic, Asymmetric Transannular Aldolizations: Total Synthesis of (+)-Hirsutene
作者:Carley L. Chandler、Benjamin List
DOI:10.1021/ja8024164
日期:2008.5.1
We report an asymmetric, catalytic transannular aldolization that provides polycyclic products useful for natural product synthesis. We found that a proline-derivative catalyzes the transannular aldol reaction of 1,4-cyclooctanediones to the corresponding cyclic beta-hydroxy ketones in good yields and with high enantioselectivities. The utility of our reaction has been demonstrated in a total synthesis