Über die «aus dem Ring»‐Claisen‐Umlagerung von Naphthalinderivaten

When a mixture of (E)‐ and (Z)‐1‐propenylnaphth‐2‐yl‐allylether ((E/Z)‐5) is heated to 182° only the (E)‐isomer rearranges to give the ‘out‐of‐ring’ product (E/Z)‐16, (Z)‐5 remains unchanged. At higher temperature (Z)‐5 yields 2‐methyl‐naphtho[2,1‐b]furane (15) as the main product. The mixture of β‐chloro‐allyl derivatives (E/Z)‐6 behaves in a similar way. These findings led us to suspect that the ‘out‐of‐ring’ products 16 and 18 are formed by direct [1, 5s] allyl migration from the starting ethers (E)‐5 and (E)‐6. Kinetic' measurements made on (E)‐ and (Z)‐5 and the independently synthesized (E)‐ and (Z)‐1‐allyl‐1‐propenyl‐1 H‐naphthalen‐2‐ones ((E)‐ and (Z)‐17) show however, that the ethers (E)‐5 and (E)‐6 undergo a double [3s, 3s] rearrangement (i.e. Claisen followed by Cope rearrangement) and hydrogen migration to yield the ‘out‐of‐ring’ products (E/Z)‐16 and (E/Z)‐18 (Scheme 9). In the (Z)‐series steric factors prevent the intermediate naphthalenones (Z)‐17 and (Z)‐19 from undergoing the Cope rearrangement and instead, at higher temperature, cleavage of the allyl group occurs (Scheme 11). The isopropenyl derivative 7 behaves in a similar way (Scheme 5). Rearrangement of (E/Z)‐1‐propenylnaphth‐2‐yl benzyl ether (8) requires a higher temperature (214°). The nature of the products obtained (Scheme 4) makes the occurrence of a direct sigmatropic [1,5s] shift of the benzyl group very unprobable. In the case of (E/Z)‐2‐propenylnaphth‐1‐yl allyl ether (10) both isomers rearrange to yield the ‘out‐of‐ring’ product 30 and the para‐Claisen product 32 (Scheme 7). This experiment also provides evidence against a sigmatropic [1,5s] shift of the allyl group. The same conclusion can be drawn from the thermal behaviour of (E/Z)‐2‐propenylphenyl allyl ether (11) and 6‐t‐butyl‐2‐propenylphenyl allyl ether (12) where only 11 yields traces of the ‘out‐of‐ring’ product 35 (Scheme 8). Up to this date there is no evidence whatsoever for the existence of a sigmatropic [1,5s] migration of an allyl group from oxygen to carbon. Thermal rearrangement of (E/Z)‐1‐propenylnaphth‐2‐yl propargyl ether (9) yields only (E/Z)‐1‐propenyl‐benz[e]indan‐2‐one (27) (and its secondary product 28). The mechanism for this reaction is given in Scheme 12. Treatment of a mixture of (E/Z)‐18 with base yields the (Z)‐cyclisation product 2,4‐dimethylnaphth[2,1‐b]oxepine (43) (Scheme 13).