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A concise five-step approach to indolizidinones 10 and 11,two advanced intermediates for the asymmetric synthesis of polyhydroxylated indolizidine alkaloids,has been developed by using N-Cbz pyrrolidin-2-yl pyridin-2-yl sulfide 13 as the chiral building block.The method features a SmI2-mediated coupling of sulfide 13 with functionalized aldehyde 14 and a tandem N-deprotection-lactamization,which constitutes a stepwise “2 + 4” annulation method for the construction of the indolizidinone ring system of 12a.
A concise five-step approach to indolizidinones 10 and 11, two advanced intermediates for the asymmetric synthesis of polyhydroxylated indolizidine alkaloids, has been developed by using N-Cbz pyrrolidin-2-yl pyridin-2-yl sulfide 13 as the chiral building block. The method features a SmI2-mediated coupling of sulfide 13 with functionalized aldehyde 14 and a tandem N-deprotection-lactamization, which results in a stepwise “2 + 4” annulation method for the construction of the indolizidinone ring system of 12a.