We prepared a variety of trans and cis di-substituted aziridine silanols to explore the scope of the cyclization reaction (Schemes 4 and 5). Aziridines were prepared using Sharpless, Che, or Kürti aziridination reactions, and most alkenyl silanols were found to be fully compatible with one of these protocols. In all cases examined, the cyclization was perfectly stereospecific. When subjected to our optimized protocol of 10 mol% Sc(OTf)3 and 1 equiv. of NaHCO3 in CH2Cl2, trans di-substituted aziridine silanols reliably gave erythro 1'-aminotetrahydrofuran products; conversely, cis di-substituted aziridine silanols gave threo products. Crystal The scale of the reaction could be increased from 0.2 mmol to 1.1 or 2.6 mmol without loss of yield or selectivity (Scheme 6A). The products were amenable to further transformations (Scheme 6B). For example, hydrogenolysis of the Cbz group of 37 formed amino tetrahydrofuran 78 in a 60% yield. With benzyl ether substrates, hydrogenation formed valuable amino-alcohol compounds 79 and 80. Interestingly, during Dess-Martin periodinane oxidation of alcohol 79, tetrahydropyridine 81 was the sole observed product rather than the expected aldehyde (Scheme 6C). What is the mechanism underlying tetrahydrofuran formation? In this transformation, why is the silanol missing in the product, which stands in contrast to what we observe with the analogous silanol epoxide? First, we must consider which oxygen of the silanol is involved in the initial SN2 attack. If the distal oxygen of the silanol is involved, one may draw a rather convoluted mechanism to explain aminotetrahydrofuran product formation, involving a series of nucleophilic attacks and silyl shifts (Scheme 7A, Pathway 1). If the distal oxygen is merely a spectator, then a simpler mechanism involving 5-exo SN2 attack by the proximal oxygen is operative (Scheme 7A, Pathway 2). As silicon nitrogen bonds are far less stable than silicon oxygen bonds, the silanol is simply cleaved during the reaction or during its quench and workup. Indeed, a significant amount of (t-Bu)2Si(OH)2 is observed by H NMR in unpurified reaction mixtures. Definitive evidence that only the proximal oxygen is involved in cyclization came from examining a series of substrates in which the silanol was replaced by TBDPS, di-tert-butyl silanoxy methyl ether, TBS, TIPS, MOM, and benzyl protecting groups (Scheme 7B, Compounds 72-77). In all cases, cyclization occurred to give 1'-amino-tetrahydrofuran 3, albeit in varying isolated yields.