Deoxygenative radical cyclization

Deoxygenative cyclization to form 5- and 6-membered rings from (O-halo aldehydes by irradiation (350 nm) and its mixture with BUjSnH and PhjP is a useful method. The cycloalkoxy radicals are captured in situ by triphenylphosphine which eliminate PhjP=0 and the carbon radicals are supplied with hydrogen from the tin hydride. Tandem radical cyclization processes are possible. 

Lactones, previously not reported as substrates for direct or indirect deoxygenation reactions, can be deoxygenated by a NaBH3CN/Bu3SnCl/AIBN combination originally utilized for the purpose of a radical cyclization reaction (eq 52). The authors reported all three reagents in combination are needed to observe the deoxygenation of the lactone carbonyl. 

Sml2 and other lanthanoid halides are often used as stoichiometric reagents in the deoxygenation of organoheteroatom oxides [88, 97], the tandem radical cyclization [140], the transformation of carbohydrates to carbocycles [140], the alkylation and arylation of perfluorinated arenes [101]. CeCl3 is used in the aldol condensation [95] ... 

The fused cyclopentane 25 has been prepared by radical cyclization via deoxygenation of 24 (Scheme 4). This ring system is a carbocyclic analogue related to the A/B ring system of the cytotoxic sesquiterpene, (+)-eremantholide. 

In Nicolaou s synthesis of aspidosphytine, the quaternary spiro center at the indole 3 position was elaborated from an alcohol, which was converted into the alkyl radical precursor xanthate 53." Upon heating in the presence of TBTH and AIBN, 53 underwent a deoxygenation and 5-exo-trig radical cyclization leading to 54 after ring closure... 

Another report by Rychnovsky et al. explored the potential of chirality transfer in the transannular cyclization of cyclodecene 45 [42], They proposed a radical deoxygenation of 45, which produces an intermediate cyclodecenyl radical that can cyclize in a 5-exo fashion to yield 5,7-fused bicycle 48 (Scheme 13). The potential for the optically enriched radical precursor 45 to undergo enantioselective cyclization is dependent on the rate of transannular cyclization. That is, if the radical generated from optically pure... 

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