Rw. Baker et al., Formal synthesis of both atropomers of desertorin C and an example of chirality transfer from a biphenyl axis to a spiro centre and its reverse, AUST J CHEM, 53(6), 2000, pp. 487-506
In connection with the synthesis of 4,4', 7,7'-tetramethoxy-5,5'- dimethyl-
6,8'-bicoumarin (desertorin C) (11) in enantiopure form, the diastereomeric
ratios of the products of the reactions between 2-isopropyloxy-6-methoxy-4
-methylphenylmagnesium bromide (24) and (4S)-4-isopropyl-2-(2,3,5-trimethox
yphenyl)-4,5-dihydrooxazole (23), between 2,4-dimethoxy-6-methylphenylmagne
sium bromide (37) and (4S)- 4- isopropyl-2-(2,3-dimethoxy-5-methylphenyl)-
4,5- dihydrooxazole (36), and between 2,4-dimethoxy-6-(t-butyldimethylsilyl
oxy)methylphenyl-magnesium bromide (46) and the oxazole (36) were explored.
The major product of the last mentioned reaction was converted into (S,4S)
-4-isopropyl-2-(2'-hydroxymethyl-4',6,6'-trimethoxy-4-methyl-1,1'-biphenyl-
6-yl)-4,5-dihydroxazole (49), the axial configuration of which was confirme
d by single crystal X-ray structural determination. The similar product (S,
4S)-2-(2', 4', 6-trimethoxy-4,6'-dimethyl-1,1'-biphenyl-6-yl)- 4,5- dihydr
ooxazole (43) was converted into (S)-1-(2,4', 6'-trimethoxy-4,6'-biphenyl-2
-yl)ethanone (57) which furnished (S)-1-(2',4',6-trimethoxy- 4,6'-dimethyl-
1,1'-biphenyl-2-yl) acetamide (58) (43%) and (S)- 2,7'-dimethoxy-3',5',6-tr
imethyl-spiro[cyclohexa-2,5-diene-1,1'-(1H) isoindole]-4-one (61) (30%) on
Schmidt rearrangement. The dienone (61) on reduction and methylation regene
rated the ketone (57). The methodology of Lipschutz was adapted for the syn
thesis of both enantiomers of 1,1'-(2',4-dihydroxy-6,6'-dimethoxy-2,4'-dime
thylbiphenyl-3,3'-diyl)bisethanone (32) and (83) which constitutes a formal
synthesis of both enantiomers of desertorin C.