Radical [n + 1] Annulations with Sulfur Dioxide

Radical cascade cyclization of 1,n-enynes and diynes for the synthesis of carbocycles and heterocycles

This review highlights recent advances in radical cascade cyclization of 1,n-enynes and diynes for the construction of carbo- and heterocycles.

A one-pot, three-step process for the diastereoselective synthesis of aminobicyclo[4.3.0]nonanes using consecutive palladium(ii)- and ruthenium(ii)-catalysis

A one-pot multi-step process that uses both Pd(ii)- and Ru(ii)-catalysis has been developed for the diastereoselective synthesis of aminobicyclo[4.3.0]nonanes.

Effect of double-bond substituents on the rate of cyclization of α-carbomethoxyhex-5-enyl radicals

Rate constants have been calculated, and compared with experimental results, for the cyclizations of 1-carbomethoxy-1-methyl-5-hexenyl radicals (2) with various substituents on C6. The calculations have been done by DFT at the B3LYP/6-311++G** level of theory. They show considerable interaction between C5 and the radical centers even in the ground state of all of the radicals 2. Experimentally, the radicals have been generated by H(•) transfer to the corresponding acrylate esters 1 and the yields of cyclized products compared to the calculated rate constants. (The "cyclized products" include those from cyclohydrogenation, 4, and those from cycloisomerization, 9.) Two phenyl substituents on C6 (2i), or a phenyl and a methyl substituent (2g, 2h), increase the rate of cyclization, but a single phenyl substituent on C6 produces a greater increase. The calculations show that the two phenyl substituents are twisted in the transition state for cyclization, while a single phenyl substituent remains flat in that transition state. A methyl substituent on C6 along with a single phenyl causes the phenyl to twist in the transition state and decreases the rate constant for cyclization below that of the H/Ph-substituted 2e, 2f.

Enantioselective Synthesis of the Tricyclic Core of FR901483 Featuring a Rh-Catalyzed [2+2+2] Cycloaddition

An efficient approach to the tricyclic framework of FR901483 is described. The sequence features a [3, 3]-sigmatropic rearrangement of a cyanate into an isocyanate, followed by its subsequent asymmetric rhodium-catalyzed [2+2+2] cycloaddition with a terminal alkyne for the synthesis of the indolizidine core. The aza-tricyclic core is completed using an intramolecular benzoin reaction to close the last ring of the natural product. Through a model study of the key cycloaddition, we evaluated the impact of different substituents on the tether of the alkenyl isocyanate.

Total synthesis of hydroxy-α- and hydroxy-β-sanshool using Suzuki-Miyaura coupling

Here, we describe the first total synthesis of hydroxyl-α- and hydroxyl-β-sanshool, which involves Suzuki-Miyaura coupling (SMC). Hydroxy-α-sanshool (1) was synthesized by SMC of bromoalkyne 4 with boronate 3 followed by (Z)-selective reduction of the triple bond in the coupling product. Hydroxy-β-sanshool (2) was synthesized by regio- and (E)-selective conversion of 4 to iodoalkene 11 followed by SMC with 3.

Formal alkylation of allenes through highly selective radical cyclizations of allene-enes

Something radical: the first example of alkene-to-allene radical cyclization of allene-enes is reported. The highly chemoselective intermolecular radical addition reaction of the alkene and subsequent, exclusive exo-radical addition to the allene was realized with perfluoroalkyl radicals. A subsequent TBAF-promoted dehydroiodination of the cyclization products forms cyclopentanes and regenerates an allene moiety (TBAF=tetra-n-butylammonium fluoride).

Synthetic Studies on the MARDi Cascade: Stereoselective Synthesis of Heterocyclic Seven-Membered Rings

[reaction: see text] A versatile stereoselective synthesis of substituted and functionalized heterocyclic seven-membered rings is described. The approach involves a formal two-carbon ring expansion of heterocyclic cyclopentanones through a base-induced anionic domino three-component transformation named the MARDi cascade leading either to oxa-, aza-, or thiacycloheptanes bearing up to five contiguous stereogenic centers.