Radical-initiated 1,2-acyloxy migration which generates a nucleoside anomeric radical

Ring-Closing Olefin Metathesis of 3,3′-(D-Glycopyranosylidene)bis(1-propene) Compounds as a Route to Anomeric Spiro Sugars

“…Radical routes to 1,2‐unsaturated sugars (glycals),24a which might explain the formation of 7 and 8 , have been found to be efficient for substrates possessing two vicinal functional groups susceptible to attack by triorganotin radicals, at C‐1 and C‐2 25. A few examples have demonstrated the formation of unsaturated sugar derivatives by radical‐mediated reductive 1,2‐elimination involving acetoxy26 and pivaloyloxy27 groups. In particular, attempted radical reduction and allylation of bromonucleoside derivatives upon treatment either with tributyltin hydride or with allyltributyltin at 80 °C produced unsaturated by‐products (< 12% yield) as a result of 1,2‐elimination of a bromine atom and a pivaloyloxy group.…”

“…In particular, attempted radical reduction and allylation of bromonucleoside derivatives upon treatment either with tributyltin hydride or with allyltributyltin at 80 °C produced unsaturated by‐products (< 12% yield) as a result of 1,2‐elimination of a bromine atom and a pivaloyloxy group. Such a 1,2‐elimination was suppressed when the radical allylation was carried out at room temperature with photochemical initiation 27. Since migration of the acetoxy group from C‐5 to C‐4 (see Schemes 1 and 3 for numbering of compounds 4 − 15 , and 21 − 25 ) took place under our conditions, as evidenced by the formation of 15 , 1,2‐elimination might presumably occur for both intermediate radicals 4R and 4′R (Scheme ) in the presence of tributyltin radicals, efficiently producing 7 upon heating (64% from 1 , 80% from 4 ).…”

Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

“…The groups of both Tanaka 67 and, shortly thereafter, Chatgilialoglu 68 have investigated the migration of the pivaloxy group in the uracil derivative 81. With tributyltin hydride as the overall reductant, Tanaka reports a ratio of 10:1.3 (∼7.5:1) in favor of the R-nucleoside, indicative of preferential quenching of the anomeric radical from the less hindered face (Table 1, entry 29).…”

Allyltributylstannane

“…Later it was reported that the 1,2-rearrangement product can also be obtained by using BF 3 ·OEt 2 as an activator on increasing its stoichiometry and the reaction temperature. 106 The other groups which undergo allylation with allyltributylstanne include -OCOOMe 107 (48) Bisfunctionalization of Activated C-C and C-X Bonds. Palladium-catalyzed bisallylation of activated olefins with allyltributylstannane proceeded in the presence of allyl chloride (eq 49).…”