A relay Rh(ii)/Pd(0) dual catalysis that enables domino [1,2]-sigmatropic rearrangement/allylic alkylation of α-diazo tertiary alcohols is described. This transformation represents a highly efficient method for the one-pot synthesis of α-quaternary β-keto-esters under mild conditions, in which two separate C-C σ-bonds at the carbenic center were formed in a straightforward manner.
Formation of spiro ketolactones versus alkoxy radical fragmentation-promoted three-atom ring enlarged lactones from cyclic ketones
作者:Alfred Hassner、Tarun K. Pradhan
DOI:10.1016/j.tetlet.2006.05.151
日期:2006.7
ketolactones 4 or of ring enlarged lactones 7 in one-step. Thus, iodination of 5–8-membered 2-allyl-2-carboethoxycycloalkanones 1a–d led, in excellent yields, to spiro ketolactones 4a–d, respectively, as single stereoisomers. On the other hand, iodination of 1a–d under alkoxy radical fragmentation conditions via incipient hemiketals produced the 8-, 9-, 10-, or 11-membered, three-atom ring enlarged, poly-functionalized
A Facile Synthesis of (n+3) and (n+4) Ring-Enlarged Lactones as well as of Spiroketolactones from n-Membered Cycloalkanones
作者:Alfred Hassner、Tarun Pradhan
DOI:10.1055/s-2007-990820
日期:2007.11
simple ethyl l-allyl-2-oxocycloalkanecarboxylates, resulting from a three-atom ringenlargement. Similarly, four-atom ringenlargements of a 5- to 9- and 6- to 10-membered-ring lactones were achieved. Alkoxy radical fragmentation (ARF) with hypervalent iodine was used as the key step for these ring expansions. The ringenlargement proceeds via an unstable hemiketal intermediate, which was isolable in some