Synthetic applications of Stryker's reagent

Abstract

(A) A catalytic quantity (≤ 5 mol% in copper) of Stryker's reagent in the presence of silanes [PhMe2SiH, MePh2SiH, or (t-Bu)Ph2SiH] is an efficient reaction condition for the reduction of non-conjugated aldehydes or ketones to the corresponding silyl ethers or alcohols (basic workup is necessary) in high yields (89-98%). (Diagram presented). (B) With Stryker's reagent, the conjugate reduction of nitroalkenes is followed by intramolecular aldol reaction (Henry reaction) to produce β-nitroalcohols in modest to good yield. (Diagram presented). (C) Stoichiometric or catalytic amounts of Stryker's reagent can be used with polymethylhydrosiloxane to promote the tandem conjugate reduction-intramolecular aldol reaction of alkynones to generate β-hydroxyenones. (Diagram presented). (D) A conjugate reduction with Stryker's reagent to form copper enolates, followed by an intramolecular aldol reaction, was used in the efficient one-pot generation of five- and six-membered carbocycles. This methodology has provided β-hydroxyketones diastereoselectively, and in good yields, at low temperatures and without the need for a dehydration step. (Diagram presented). (E) Stryker's reagent allows for the stoichiometric conjugate reduction of α,β-unsaturated ketones or lactones without affecting isolated alkenes, carbonyl groups, halogens or typical oxygenated functionalities under the reaction conditions. (Diagram presented). (F) Selective reduction of alkynes to the corresponding alkenes can also be achieved with Stryker's reagent. Terminal alkynes are reduced at room temperature, while unactivated internal alkynes react only at elevated temperatures. Protection of propargylic alcohol functionality is usually unnecessary, although in sterically hindered cases, fragmentation is sometimes competitive. (Diagram presented). © Georg Thieme Verlag Stuttgart.