Radical Cyclization of Polyenes Initiated by Attack of Trialkyltin or Germanium Radical on an Ynone

Abstract

Scheme 2 Scheme 3Notes

Catalytic tin radical mediated tricyclisations. Part 1. Monocyclisation studies †

“…Pancrazi and co-workers 14 achieved elimination of the initiating tri-nbutyltin radical in an alkyne-alkene monocyclisation as did Spino and Barriault with the tricyclisation of an acyclic alkynone diene. 15 Marco-Contelles accomplished tricyclisation of an alkynic diene sugar 16 closely resembling our original report. Palladium catalysed cyclisation of similar substrates has only yielded bisannulation products thus far.…”

“…On the other hand use of hexabutylditin with various initiators is much less efficient as has been noted by others. 15 TBTH (1.3 equiv.) in benzene was added dropwise from a syringe pump to a refluxing solution containing the enediyne 9 and AIBN (0.04 equiv.)…”

Synthetic Scope and Mechanistic Studies of Ru(OH)x/Al2O3‐Catalyzed Heterogeneous Hydrogen‐Transfer Reactions

“…Mass spectra were recorded on a Shimadzu GCMS‐QP2010 equipped with a DB‐WAX capillary column (internal diameter=0.25 mm, length=30 m) at an ionization voltage of 70 eV. Reagents, solvents, and substrates, except for 21 a , 22 a , ( S )‐ 23 a , ( S )‐ 24 a , 25 a , and 26 a , which were synthesized according to the literature procedures (see Supporting Information),8c, 25–27 were purchased from Tokyo Kasei, Aldrich, and Fluka (reagent grade) (the solvents in particular must be carefully purified). Alumina (KHS‐24, BET surface area: 160 m 2 g −1 ) was supplied by Sumitomo Chemical Co., Ltd. All products were identified by comparison of their GC retention time, mass spectra, and 1 H and 13 C NMR spectra with authentic samples.…”

Enantioselective Intramolecular [2+2+2] Cycloaddition of Dienynes for the Construction of Adjacent Three Chiral Centers

“…7 On the contrary, as for the cycloaddition of dienynes (Scheme 1), rutheniumcatalyzed 8 and chiral rhodium-catalyzed reactions 9 of ene-yne-enes (type A) were reported, however, the cycloaddition of yne-ene-enes (type B) was not reported. The transformation of yne-ene-enes into tricyclic cyclohexenes was realized by palladium-catalyzed cycloisomerization along with thermal Diels-Alder reaction 10 and radical cyclization, 11 but no asymmetric variant was reported. 12 We examined an intramolecular [2+2+2] cycloaddition of yne-ene-enes: oxidative coupling of enyne moiety, which is more active than diene moiety, proceeds with a metal catalyst, and the following alkene insertion provides a tricyclic cyclohexene with adjacent three chiral centers (Scheme 2).…”