77609-88-2Relevant articles and documents
Claisen Rearrangement of 7-(3'-Methylbut-2'-enyloxy)flavones and Isoflavones
Subba Raju, K. V.,Sudha, K.,Srimannarayana, G.
, p. 866 - 870 (2007/10/02)
The Claisen rearrangement of 7-(3'-methylbut-2'-enyloxy)-3-methylflavone (IIb) in N,N-dimethylaniline yields an abnormal open-chain product 7-hydroxy-8-(1',2'-dimethylallyl)-3-methylflavone (IIIb), the normal cyclisation product 2",3"-dihydro-2",3",3",3-tetramethylfuroflavone (Vb) and 2",3"-dihydro-2",2",3",3-tetramethylfuroflavone (VIb).Rearrangement of IIb in vacuo yields 7-hydroxy-3-methylflavone (Ib) and VIb.The Claisen rearrangement of IIb in Ac2O-NaOAc gives 7-acetoxy-8-(1',1'-dimethylallyl)-3-methylflavone (VIIIb) which on alkaline hydrolysis yields 7-hydroxy-8-(1',1'-dimethylallyl)-3-methylflavone (VIIb) (normal open-chain product).Claisen rearrangement of VIIb gives a mixture of IIIb, Vb and VIb.Rearrangement of 7-(3'-methylbut-2'-enyloxy)flavone (IIa) in N,N-dimethylaniline furnishes 7-hydroxy-8-(1',2'-dimethylallyl)flavone (IIIa) and 2",3"-dihydro-2",3",3"-trimethylfuroflavone (Va).Under similar conditions 7-(3'-methylbut-2'-enyloxy)-3-phenylflavone (IIc) and 7-(3'-methylbut-2'-enyloxy)-2-methylisoflavone (IId) yield only 2",3"-dihydro-2",3",3"-trimethylfuro derivatives (Vc) and (Vd) respectively.Acid-catalysed cyclisation of IIIa, IIIb and VIIIb gives VIa, VIb and Vb respectively.In all the Claisen rearrangements, only the angular rearrangement products (i.e. rearrangement to 8-position of flavonoid nucleus) are isolated.It is believed that unstable 7-hydroxy-8-(1',1'-dimethylallyl) compound (VII) acts as an intermediate for the formation of III, V and VI.
