Efficient 1,2-Asymmetric Induction in Radical Reactions: Stereoselective Radical Addition to 3-Hydroxy-1-(methylthio)-1-(p-tolylsulfonyl)-1-alkenes

Photocatalysis for the Formation of the C−C Bond

“…Thus, some chiral 3-hydroxy-1-(methylthio)-1-(p-tosyl)-1-alkenes gave the corresponding 1-hydroxyalkyl derivatives by BP (1 mol equiv) photocatalysis in methanol and in i-propanol with high syn selectivity (typically, syn/anti ) 95:5), indicative of a high asymmetric induction in this acyclic system. 125 Likewise, the BP (15% mol equiv) photocatalyzed alkylation has been applied to a pair of 1,3-dioxin-4-ones incorporating (-)-menthone as a chiral auxiliary in position 2. It was found that the radical from i-propanol was added from the more exposed a-side with complete selectivity, although in a low yield (again, attack by dialkylcuprate occurred from the opposite face).…”

“…Because of the mild photocatalytic conditions, a good stereoselectivity could be obtained in several cases. Thus, some chiral 3-hydroxy-1-(methylthio)-1-( p -tosyl)-1-alkenes gave the corresponding 1-hydroxyalkyl derivatives by BP (1 mol equiv) photocatalysis in methanol and in i -propanol with high syn selectivity (typically, syn / ant i = 95:5), indicative of a high asymmetric induction in this acyclic system . Likewise, the BP (15% mol equiv) photocatalyzed alkylation has been applied to a pair of 1,3-dioxin-4-ones incorporating (−)-menthone as a chiral auxiliary in position 2.…”

Photochemical Alkylation of Ketene Dithioacetal S,S-Dioxides. An Example of Captodative Olefin Functionalization

“…Another stoichiometric method for generating a radical is photochemical hydrogen abstraction by means of an nπ* triplet, e.g., benzophenone . Ogura reported the high yield functionalization of ketene thioacetal S , S -dioxides with various hydroxy (alkoxy)alkyl radicals generated from alcohols or ethers by irradiation with an equimolecular amount of benzophenone. , We explored whether the same scheme could be applied to hydrocarbons possessing no activated C−H bond. As it appears from Table and Scheme the result was positive.…”

“…Ketene dithioacetal S , S -dioxides, as an example, are easily prepared; β-alkylation of such derivatives may lead to highly substituted α-thiosulfones. These, in turn, are convenient synthetic intermediates in view of several possible elaborations, e.g., C -alkylation and -arylation, substitution of an allyl for a sulfone group, desulfurization, , pyrolysis to yield a carbonyl derivative, Pummerer rearrangement . Ketene dithioacetal S , S -dioxides have been shown to act as efficient acceptors of carbenes as well as of 1-hydroxy- (or alkoxy-)alkyl radicals. , Furthermore, intramolecular radical addition of β-(ω-iodoalkyl) derivatives has been shown to occur under classic radical chain conditions yielding five-, six-, and also four-membered cyclic derivatives, a result rationalized on the basis of the peculiar stability of the adduct radical due to the captodative effect .…”

The past, present, and future of the Yang reaction

“…[23][24][25][26][27] In addition, other than the ester group, nitro, sulfone, amide, nitrile, and aldehyde groups can all be used as activating groups for the radical acceptors. [28][29][30][31][32] Addition of radicals to substituted butenolides has also been shown to proceed with good diastereoselectivity. [33][34][35][36] For example, Mann reported in 1994 that irradiation of butenolide 37 with 10 in methanol gave γ-lactone 38 as the only diastereomeric product (Fig.…”