Construction of oxocane skeleton via unusually regioselective CC bond forming cyclization: Synthesis of (+) and (−)-lauthisan

Preparation of Oxocanes by Electrophilic Cyclizations of Unsaturated Alcohols in the Presence of Bis(collidine)halonium(I) Hexafluorophosphates

“…After 12 h at room temp., the solvent was removed under vacuum. The residue was purified by chromatography on silica gel (diethyl ether/ pentane, 30:70) to give 2.000 g (75%) of methyl 2-(pent-4-enyl)benzoate (14). 1 Methyl 3-(2-Vinylphenyl)propanoate (16): nBuLi (1.6  solution in hexane, 87.50 mL) was added at Ϫ20°C under argon to a suspension of methyltriphenylphosphonium bromide (50.300 g, 0.14 mol) in THF (150 mL).…”

“…[1] Many reactions have been examined, with greater or lesser degrees of success. Among the most promising we can cite the rhodium carbenoid cyclization of α-diazocarbonyl compounds [2] (reported yields were in the 40Ϫ73% range), the nucleophilic cyclization of iodides, [3] epoxides, [4] and esters [5] (60Ϫ87%), the cyclization of hexacarbonyldicobalt complexes [6] (43Ϫ84%), the cyclization of allylsilanes with methoxymethyl ethers [7] (53%), the cyclization of allyltin compounds with acetals [8] and of allylboranes with aldehydes [9] (30Ϫ35%), the cyclization of olefins with acetals [10] or thioacetals [11] induced by titanium salts or other Lewis acids (50Ϫ70%), radical cyclization with terminal double bonds [12] (40Ϫ50%), the reaction of alcohols with thioacetals [13] (55%), the palladium-induced cyclization of allyl carbonates [14] (74%), and the metathesis of dienes in the presence of ruthenium [15] and molybdenum [16] complexes (26Ϫ95%). We recently reported an efficient method for the preparation of oxepanes by electrophilic cyclization of 6-hepten-1-ols [17] in the presence of bis(collidine)iodonium() hexafluorophosphate as electrophile.…”

Mn-, Fe-, and Co-Catalyzed Radical Hydrofunctionalizations of Olefins

“…Consequently, we do not discuss these numerous reactions further except to state that a number of groups have found uses for this reaction in complex molecule and natural product syntheses. 207,208,386,387,388,389,390,391 …”

Second‐Generation Total Synthesis of Spirastrellolide F Methyl Ester: The Alkyne Route

“…15 Its elaboration to the isopropylidene acetal 17 , which later plays an essential role as a conformational control element for setting the stereocenter at C24,7b was uneventful, as was the conversion of the methyl ester group into the required enol triflate 21 . This transformation was best achieved by addition of lithiated methyl phenyl sulfone16 and subsequent cleavage of the PhSO 2 group in 18 under free‐radical conditions; the resulting ketone 19 then gave triflate 21 on deprotonation with LiHMDS and quenching of the generated enolate with triflimide 20 as the preferred electrophile 17…”