Pithani V. Subhash

TRANSFORMATIONS OF LIGNANS, PART V. REACTIONS OF DDQ WITH A GMELINOL HYDROGENOLYSIS PRODUCT AND ITS DERIVATIVES

Hydrogenolysis of gmelinol 8 with sodium in liquid ammonia gives a triol 9, which is converted under various reaction conditions into a range of derivatives including the di- and tri-O-methyl ethers 10 and 11, a 3,4-dibenzyl-3-hydroxy-tetrahydrofuran 12, and its acetate 13. These derivatives undergo oxidative cyclisation with DDQ in acetic acid or trifluoroacetic acid to yield 1-aryltetralin, 1-arylnaphthalene, dibenzocyclooctadiene and spirodienone derivatives in reactions which provide biomimetic analogies for biogenetic transformations of lignans.

Transformations of lignans. Part 4: Oxidative and reductive rearrangements of dibenzocyclooctadiene and spirodienone lignans

DDQ oxidation of a dibenzocyclooctadiene derived from a 2,3-dibenzylbutane-1,2,4-triol di-O-methyl ether gives an oxygen-bridged dibenzocyclooctadienone and an oxygen-bridged spirodienone. The same products may also be obtained directly from the dibenzylbutane derivative by treatment with excess DDQ. Acid treatment of the spirodienone leads to demethylation and rearrangement to an ortho-benzoquinone. Reductive rearrangement of the spirodienone produces an oxygen-bridged dibenzocyclooctadienone. These reactions yield unique cyclohexadienone lignans and illustrate readily achieved increases in complexity starting from a simple dibenzylbutane derivative.

TRANSFORMATIONS OF LIGNANS, PART IV. ACID-CATALYSED REARRANGEMENTS OF GMELINOL WITH BF3-ETHERATE AND STUDY OF A PRODUCT WITH A UNIQUE LIGNAN SKELETON FORMED BY FURTHER OXIDATION WITH DDQ

Abstract Reaction of gmelinol 1 with BF3-etherate followed by treatment with various additives gave two isomeric products 2 and 5 formed by rearrangement of the 2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane skeleton. Compounds 2 and 5 on oxidation with DDQ in trifluoroacetic acid or benzene produced enantiomers 8 and ent-8 respectively, which have a “distorted furofuran” skeleton. Compound 5 on reduction with triethylsilane and BF3-etherate gave 13, which is isomeric with di-O-methyl cycloolivil.