Variable-temperature NMR studies of 6-(o-tolyl)-8-methoxy-1,8-dimethylbicyclo[2.2.2]oct-5-en-2-ones

Variable temperature NMR studies, establishing the presence of atropisomers, of β-(o-tolyl)-carvone (2) and the bicyclo[2.2.2]octene derivatives 4 and 5 mentioned in the title are described

Radical cyclisation based approach to lignans. Synthesis of 4-arylmethyldihydrofuran-2-ones

Bromoacetalisation of the cinnamyl alcohols 7a-d, obtained from the corresponding benzaldehydes, generated the bromoacetals 10a-d. The 5-exo trig radical cyclisation of the bromoacetals 10a-d followed by one step hydrolysis-oxidation of the resulting cyclic acetals 11a-d furnished the title compounds 6a-d, respectively, well-established intermediates of a variety of lignans

Radical annulation vs the 3-exo-trig cyclization via fine tuning of the substrate structure

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Synthesis of chiral bicyclo[2.2.2]octa-5,7-dien-2-ones1ones^1

Reaction of the methoxyenones 3 and 11 with an excess of boron trifluoride etherate furnishes cleanly the chiral bicyclo[2.2.2]octa-5,7-dien-2-ones 9 and 12 respectively

Radical Cyclization Methodology to Lignans: Synthesis of (.+-.)- Enterolactone

Synthesis of enterolactone, the first lignan of human origin, starting from 3-methoxycinnamyl alcohol employing a 5-exo-trig radical cyclisation reaction of mixed bromoacetal as the key step is described

A formal total synthesis of (+/-)-enterolactone

A radical cyclization based methodology has been applied for the formal total synthesis of (+/-)-enterolactone (1), the first lignan isolated from human source. Bromoacetalization reaction of the cinnamyl alcohols 7 and 13 using ethyl vinyl ether and NBS, generated the bromoacetals 8 and 15. The 5-exo-trig radical cyclization reaction of the bromoacetals 8 and 15 with in situ generated catalytic tri-a-butyltin hydride and AIBN furnished a 3 : 2 diastereomeric mixture of the cyclic acetals 9 and 16. Sonochemically accelerated Jones oxidation of the cyclic acetals 9 and 16 yielded the gamma-butyrolactones 10 and 12 completing the formal total synthesis of (+/-)-enterolactone. Alternatively radical cyclization of the bromoacetate 17 furnished a 1 : 2 mixture of the lactone 10 and the reduced product 18