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).