Epoxy silyl ether rearrangements: a new, stereoselective approach to the synthesis of .beta.-hydroxy carbonyl compounds

Chemoenzymatic Synthesis of Advanced Intermediates for Formal Total Syntheses of Tetrodotoxin

“…Zuschriften resident hydrogen atom into ap seudo-axial orientation (Figure 3). Indeed, upon exposure of 25 to TiCl 4 , [22] the desired hydride shift took place smoothly,p roducing 27 and 4 in a4 :1 ratio as the major products,w ith the required stereochemistry at the newly formed C4a tertiary carbon center (Scheme 6 [23] was then obtained by MOM protection of 4 with dimethoxymethane in the presence of phosphorus(V) oxide.T hus Satos intermediate was synthesized in ten steps from 6.…”

3.16 The Semipinacol Rearrangements

“…For example, Marson Another type of Lewis acid which could effectively promote (catalyze) the semipinacol rearrangement is silyl reagent. Right after their report of the epoxy silyl ether rearrangements under the Lewis acidic conditions (Scheme 65), 79 Suzuki et al developed a catalytic version by using TMSX (X ¼OTf, I), which generally gave better results than the stoichiometric conditions. 80 Because of the special reaction mechanism and chemical property of TMSX, the catalyst could be regenerated during the course of the rearrangement (Scheme 66).…”

“…Conversely, a mixture of two isomers will most likely be formed if substrates with two substituents having similar migration aptitude are used. 79 …”

“…They first developed the 1,2-rearrangement of epoxy silyl ether compounds, which gave a new method toward the synthesis of b-hydroxy carbonyl compounds. 79 Subsequently, a different rearrangement pattern was achieved by varying the structure of the substrate and the catalyst (Scheme 80). 80 These transformations are highly stereoselective and site-specific.…”

“…79 The reduction process also can be achieved using Meerwein-Pondorf-Verley reaction. Tu et al successfully converted epoxy alcohols into 1,3-diols using Al(OPr i ) 3 and Pr i OH (Scheme 96).…”