Intramolecular hydrosilation of .alpha.-hydroxy enol ethers: a new highly stereoselective route to polyhydroxylated molecules

Abstract

Stereoselective chemical synthesis of carbohydrates constitutes a large and challenging field in modern synthetic organic chemistry.2 Among a wide variety of methodologies for stereoselective construction of polyoxygenated skeletons,3 that being the most straightforward is the stereoselective introduction of two oxygen functionalities to the carbon-carbon double bonds (Scheme I, route a), as represented by the Sharpless epoxidation4 or osmium tetroxide oxidation of allyl alcohols.3h•5 An alternative route may be achieved by anti-Markownikoff hydration of enol ether counterparts (Scheme I, route b), but such an approach has so far been rarely studied.6(1) Silafunctional compounds in organic synthesis. 39.

The Evolution of the Total Synthesis of Rocaglamide

“…The conversion of 1 to morpholino enamide 2 was straightforward. Deprotonation of ethyl vinyl ether by tert ‐butyllithium, followed by trapping of ethoxyvinyllithium by 2 led to dienone 3 . Exposure of 3 to catalytic [PdCl 2 (MeCN) 2 ] complex in acetone, led to α‐hydroxycyclopentenone 4 in 67 % yield for the two steps from 2 .…”

Silicon-Based Cross-Coupling Reactions Through Intramolecular Activation

“…Alternatively, simple alkenylsilanes such as vinyl and propenylsilanes in addition to a number of arylsilanes and heteroar ylsilanes, can be prepared by the ring opening reactions of cyclic silyl ethers 6 with highly nucleophilic organolithium or magnesium reagents (Table 2). A cyclohexane variant of cyclic silyl ether 6 , which was readily prepared through O silylation of 2 hydroxyprop 2 yl substituted cyclohexene followed by platinum catalyzed intramolecular hydrosilylation, 19 also reacts with aryl Grignard reagents to give the corresponding arylsilanes 2 in good yields (Scheme 6). The trans stereochemistry of the arylsilyl group and the 2 hydroxylprop 2 yl functionality has been unambiguously con rmed by X ray crystallography of a related 3,5 dinitrobenzoate.…”

Generation and reactivity of α-metalated vinyl ethers

“…20 In addition to this principal hydrolysis protocol, other reactions of the vinyl ethers have been described (Scheme 15) including ozonolysis to the corresponding ester 57, 30,32,43,53,59,75 treatment with OsO 4 or MCPBA to generate α-hydroxy ketones 58 [44][45][46][47]84 and exposure to NBS or NCS to produce α-halo ketones 59. 38,64 Intramolecular hydrosilylation to provide syn diols 60 (Scheme 16), 29 tandem cationic aza-Cope rearrangement-Mannich cyclization, 49 Claisen-Johnson rearrangement yielding γ-keto esters 61 (Scheme 16), 31 intramolecular [2 ϩ 2] photocyclization 40, 41 and intramolecular π-allylpalladium catalyzed cyclization 77 are other reactions that have been reported for the vinyl ether products 14 generated from the reactions of MVL and EVL. Many of these reactions are key steps in the synthesis of natural products including the allopumiliotoxin A alkaloids 267A and 339B, 48 the terpenes silphinene 61 and α-cedrene, 40,41 and taxusin.…”