SmI2-mediated radical cross-couplings of α-hydroxylated aza-hemiacetals and N,S-acetals with α,β-unsaturated compounds: asymmetric synthesis of (+)-hyacinthacine A2, (-)-uniflorine A, and (+)-7-epi-casuarine.

The SmI(2)-mediated radical coupling reactions of β-hydroxylated pyrrolidine/piperidine aza-hemiacetals 8 and 9 and N,S-acetals 6 and 33 with α,β-unsaturated compounds are described. This method allows a rapid access to β-hydroxylated pyrrolidines, piperidines, pyrrolizidinones, and indolizidinones. Starting from N,S-acetal 33 and via a common intermediate 27, the alkaloids hyacinthacine A(2) (2), uniflorine A (3, 6-epi-casuarine), and the unnatural epimer 7-epi-casuarine (37) have been synthesized in four and five steps with overall yields of 34%, 16%, and 13%, respectively.

One-pot cross-coupling of N-acyl N,O-acetals with alpha,beta-unsaturated compounds.

The synergistic action of BF(3).OEt(2) and SmI(2) allowed a series of intermolecular cross-couplings of readily available N-acyl N,O-acetals with alpha,beta-unsaturated compounds to be performed in high yields, which was applied to the stereoselective synthesis of pyrrolizidine alkaloid (+)-xenovenine.

[Continuous observation of canal aberrations in S-shaped simulated root canal prepared by hand-used ProTaper files].

Purpose: To observe the formation of canal aberrations in S-shaped root canals prepared by every file of hand-used ProTaper.

Methods: Fifteen S-shaped simulated resin root canals were selected. Each root canal was prepared by every file of hand-used ProTaper following the manufacturer instruction.