Titanocene-Catalyzed Reduction of Lactones to Lactols

Abstract

A convenient method for the conversion of lactones to lactols is described. The hydrosilylation to lactols is carried out via air-stable titanocene difluoride or a titanocene diphenoxide precatalyst using inexpensive polymethylhydrosiloxane (PMHS) as the stoichiometric reductant. These procedures have been demonstrated with a variety of substrates and proceed in good to excellent yield.

Towards a Library of “Early‐Late” Ti–Ru Bimetallic Complexes

“…The halide exchange proceeded smoothly and led to the titanocene difluoride phosphanes 5, and 6, respectively, in very good yields. TiH], which has proved to be a very effective catalyst for the hydrosilylation of lactones [12] and the dehydropolymerisation of silanes. [13] The potential of the bimetallic complexes constructed with the fluorinated titanocene phosphane is thus reinforced.…”

Synthesis of 5-O-benzyl-2-C-β-fluoromethyl-1,2,3-tri-O-acetyl- D-ribofuranose

“…11 In our own hands, benzylation proceeded more cleanly and rapidly with sodium hydride and benzyl bromide in dimethylformamide rather than tetrahydrofuran solvent. We then sought a convenient method to reduce 13 to lactol (14). Although this can be achieved with diisobutylaluminium hydride at low temperature, precedent suggested a significant excess of reagent would be required, which is disadvantageous when working on a large scale.…”

“…12 We were therefore drawn to Buchwald's hydrosilylation, which is achieved by using inexpensive polyhydromethylsiloxane and a number of titanium catalysts under ambient conditions. 13,14 We chose dicyclopentadienyltitanium difluoride as the catalyst since it is easy to prepare from the commercially available dichloride and sodium fluoride in water at 50°C, followed by thorough drying.…”

“…With lactol (14) in hand, we then performed an aldol reaction with aqueous formaldehyde to give 15 as a single stereoisomer at C-2 in 55% yield. This transformation has been described for the related 5-O-trityl derivative.…”

Reduction of Aromatic and Aliphatic Esters Using the Reducing Systems MoO2(acac)2 or V(O)(OiPr)3 in Combination with 1,1,3,3‐Tetramethyldisiloxane

“…Among these derivatives, polymethylhydrosiloxane (PMHS), as a 40-unit polymeric chain, was used with titanium complexes by Buchwald and Lawrence. According to studies by Buchwald, the reduction of lactones to lactols [29] can be performed with [Cp 2 TiX 2 ] or [Cp 2 Ti(OPh) 2 ], and alcohols can be prepared from esters [30] with [Ti(OiPr) 4 ] with good selectivity toward alkenes, epoxides, and halides. The latter process was studied in stoichiometric quantities by Lawrence.…”