It is shown in this Part 2 that heptaleno[1,2-c]furans 1 react thermally in a Diels -Alder-type [4 þ 2] cycloaddition at the furan ring with vinylene carbonate (VC), phenylsulfonylallene (PSA), a-(acetyloxy)acrylonitrile (AAN), and (1Z)-1,2-bis(phenylsulfonyl)ethene (ZSE) to yield the corresponding 1,4-epoxybenzo[d]heptalenes (cf. Schemes 1, 5, 6, and 8). The thermal reaction of 1a and 1b with VC at 1308 and 1508, respectively, leads mainly to the 2,3-endo-cyclocarbonates 2,3-endo-2a and -2b and in minor amounts to the 2,3-exo-cyclocarbonates 2,3-exo-2a and -2b. In some cases, the (P*)-and (M*)-configured epimers were isolated and characterized (Scheme 1). Base-catalyzed cleavage of 2,3endo-2 gave the corresponding 2,3-diols 3, which were further transformed via reductive cleavage of their dimesylates 4 into the benzo[a]heptalenes 5a and 5b, respectively (Scheme 2). In another reaction sequence, the 2,3-diols 3 were converted into their cyclic carbonothioates 6, which on treatment with (EtO) 3 P gave the deoxygenated 1,4-dihydro-1,4-epoxybenzo[d]heptalenes 7. These were rearranged by acid catalysis into the benzo[a]heptalen-4-ols 8a and 8b, respectively (Scheme 2). Cyclocarbonate 2,3endo-2b reacted with lithium diisopropylamide (LDA) at À 708 under regioselective ring opening to the 3-hydroxy-substituted benzo[d]heptalen-2-yl carbamate 2,3-endo-9b (Scheme 3). The latter was Omethylated to 2,3-endo-(P*)-10b. The further way, to get finally the benzo[a]heptalene 13b with MeO groups in 1,2,3-position, could not be realized due to the fact that we found no way to cleave the carbamate group of 2,3-endo-(P*)-10b without touching its 1,4-epoxy bridge (Scheme 3).The reaction of 1a with PSA in toluene at 1208 was successful, in a way that we found regioisomeric as well as epimeric cycloadducts (Scheme 5). Unfortunately, the attempts to rearrange the products under strong-base catalysis as it had been shown successfully with other furan -PSA adducts were unsuccessful (Scheme 4).The thermal cycloaddition reaction of 1a and 1b with AAN yielded again regioisomeric and epimeric adducts, which could easily be transformed into the corresponding 2-and 3-oxo products (Scheme 6). Only the latter ones could be rearranged with Ac 2 O/H 2 SO 4 into the corresponding benzo[a]heptalene-3,4-diol diacetates 20a and 20b, respectively, or with trimethylsilyl trifluoromethanesulfonate (TfOSiMe 3 / Et 3 N), followed by treatment with NH 4 Cl/H 2 O, into the corresponding benzo[a]heptalen-3,4-diols 21a and 21b (Scheme 7).The thermal cycloaddition reaction of 1 with ZSE in toluene gave the cycloadducts 2,3-exo-22a and -22b as well as 2-exo,3-endo-22c in high yields (Scheme 8). All three adducts eliminated, by treatment with base, benzenesulfinic acid and yielded the corresponding 3-(phenylsulfonyl)-1,4-epoxybenzo[d]heptalenes 25. The latter turned out to be excellent Michael acceptors for H 2 O 2 in basic media (Scheme 9). The Michael adducts lost H 2 O on treatment with Ac 2 O in pyridine and gave the 3-(phenylsulfonyl)benzo[d]heptalen-2-ones ...
