Dedicated to Oscar Jeger on the occasion of his 80th birthday (7. v. 97) Benzo [a]heptalene has been synthesized by two different approaches. The first one follows a pathway to hexahydrobenzo [a]heptalenone 19a that has been already described by Wenkert and Kim (Scheme f). Indeed, 19a was obtained in a mixture with its double-bond-shifted isomer 19b. Reduction of this mixture to the corresponding secondary alcohols 26a/26b and elimination of H,O lead to a mixture of the tetrahydrobenzo[a]heptalenes 23a-d (Scheme 7 and 8). Reaction of 23a-d with 2 equiv. of triphenylmethylium tetrafluoroborate in boiling CHCl,, followed by treatment with Me,N in CH,CI,, generated directly 2, unfortunately in a mixture with Ph,CH that could not be separated from 2 (Scheme 10 and ff). The second approach via dimethyl benzo[u]heptalene-6,7-dicarboxylate (30) (Scheme fZ) that was gradually transformed into the corresponding carbaldehydes 37 and 43 (Scheme 14) both of which, on treatment with the Wilkinson catalyst [RhCl(PPh,),] at 130" in toluene, smoothly decarbonylated, finally gave pure 2 as an unstable orange, viscous oil. UV/VIS, NMR, and mass spectra of 2 are discussed in detail (cf. Chapt. 3).

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A simple new method has been devised for the preparation of α-isothiocyanatoethers 1a-1f in good yields by reaction of PO(NCS)3 or (PhO)2PONCS with an equimolar mixture of aldehydes and alcohols. The course of nucleophilic additions of methanol, amines and hydrazine to 1a-1f is described.

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