(±)‐Lysergic acid (1) has been synthesized from 4‐hydroxymethyl‐1‐tosylindole (2) by a sequence of 9 steps. The crucial thermolysis 9 → 10 involves the in situ‐generation of the transient diene III which undergoes an intramolecular cycloaddition to a C, N‐double bond at 200° and at low stationary concentration of III.

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(±)‐α‐Acoradiene (4) has been synthesized from 3‐methoxy‐2‐cyclohexenone by a sequence of 8 steps. The key steps (Scheme 6) are the regio‐ and stereoselective photo[2+2]addition 7→6 and the reductive fragmentation 6→5.

k )-Modhephene (6) has been synthesized from the easily available trimethylpentalenone 1 in 6 steps in 26% overall yield (Scheme 2). The remarkably smooth 1,4-addition/enolate trapping 1 -+ 2 and subsequent selenoxide elimination after oxidation furnished the key intermediate 3 which underwent an expedient and highly stereoselctive intramolecular ene-reaction to give the propellane 4, readily convertible to (k )-6.In conjunction with a general program exploring the scope and limits of intramolecular ene-reactions [ 11 we have observed previously that 1,6-dienes with the H-donor site cis relative to the enophile cyclize thermally to give exclusively 5membered rings containing cis-related H-donor and acceptor sites [2]. These results could be rationalized by inspection of the alternative transition states A and B; whereas A shows a severe angle strain, B is perfectly attainable (Scheme I ) . Scheme 1As published in a recent short communication we have exploited these findings for a stereoselective synthesis of the naturally occurring propellane modhephene (6) [3]. Modhephene, isolated by Zalkow et al. from rayless goldenrod (Isocoma wrightii) [4] and by Bohlmann et al. from South African Berkheya species [5] has attracted considerable attention as a target for synthesis. However all synthetic I )

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