Syntheses of isochromane analogues of the michellamines and korupensamines

Syntheses of the oxygen analogues 6, 7 and 8 of the michellamines 1 and korupensamines 2 are described. Racemic 5-iodo-6,8-dimethoxy-trans-1,3-dimethylisochromane 10 was synthesised in eleven steps from 2,4-dimethoxybenzaldehyde in an overall yield of 51%. The isopropoxy analogue 11 was synthesised in a similar manner. Isochromane 10 was coupled using Suzuki methodology with 4-isopropoxy-5-methoxy-7-methylnaphthalene-1-boronic acid 9 to produce 7 in 96% yield. This was converted in good yield into the desired product 6 by oxidative dimerisation followed by reduction of the cross-conjugated ene-dione intermediate 45.