202286-64-4Relevant academic research and scientific papers
Reductive elimination of phenylsulfonyl groups in the 3-position of benzo[a]heptalene-2,4-diols
Fattah, Mohy Eldin Abdel,El Rayes, Samir,Soliman, El Sayed Ahmed,Linden, Anthony,Abou-Hadeed, Khaled,Hansen, Hans-Juergen
, p. 1085 - 1101 (2007/10/03)
3-(Phenylsulfonyl)benzo[a]heptalene-2,4-diols 1 can be desulfonylated with an excess of LiAlH4/MeLi · LiBr in boiling THF in good yields (Scheme 6). When the reaction is run with LiAlH4/MeLi, mainly the 3,3′-disulfides 6 of the corresponding 2,4-dihydroxybenzo[a]heptalene-3- thiols are formed after workup (Scheme T). However, the best yields of desulfonylated products are obtained when the 2,4-dimethoxy-substituted benzo[a]heptalenes 2 are reduced with an excess of LiAlH4/TiCl 4 at - 78 → 20° in THF (Scheme 10). Attempts to substitute the PhSO2 group of 2 with freshly prepared MeONa in boiling THF led to a highly selective ether cleavage of the 4-MeO group, rather than to desulfonylation (Scheme 13).
On the Formation of 2-Sulfonylbenzo[a]heptalene-1,3-diols as Precursors for the Synthesis of Colchicinoids
Abou-Hadeed, Khaled,Hansen, Hans-Juergen
, p. 4018 - 4047 (2007/10/03)
The benzo[a]heptalene formation from 4-[(R-sulfonyl)acetyl]heptalene-5-carboxylates 15 and 5-[(R-sulfonyl)acetyl]heptalene-4-carboxylates 16 (R = Ph or morpholino) in the presence of R′SO2CH2Li and BuLi has been investigated (Scheme 6). Only the sulfonyl moiety linked to the C=O group at C(4) of the heptalene skeleton is found at C(3) of the formed benzo[a]heptalene-2,4-diols 3 in accordance with the general mechanism of their formation (Scheme 3). Intermediates that might rearrange to corresponding 2-sulfonylbenzo[a]heptalene-1,3-diols lose HO-under the reaction conditions to yield the corresponding cyclopenta[d]heptalenones of type 11 (Schemes 6 and 7). However, the presence of an additional Me group at C(a) of the lithioalkyl sulfones suppresses the loss of HO-, and 4-methyl-2-sulfonylbenzo[a]heptalene-1,3-diols of type 4c have been isolated and characterized for the first time (Schemes 8 and 10). A number of X-ray crystal-structure analyses of starting materials and of the new benzo[a]heptalenes have been performed. Finally, benzo[a]heptalene 4c has been transformed into its 1,2,3-trimethoxy derivative 23, a benzo[a]heptalene with the colchicinoid substitution pattern at ring A (Scheme 11).
Studies for a variable synthesis of colchicinoids: Construction of ring a on a heptalene moiety
Meyer, Markus,Abou-Hadeed, Khaled,Hansen, Hans-Juergen
, p. 2383 - 2397 (2007/10/03)
It is shown that heptalene-4,5-dicarboxylates 2, which react with lithiated methyl sulfones mainly in a Michael fashion at C(3) (cf. Scheme 2), so that the formation of 3-sulfonylbenzo[a]heptalene-2,4-diols 5 is repressed or completely suppressed, can be
A 'One-Pot' Anellation Method for the Transformation of Heptalene-4,5-dicarboxylates into Benzo[a]heptalenes
Abou-Hadeed, Khaled,Hansen, Hans-Juergen
, p. 2535 - 2564 (2007/10/03)
It has been found that dimethyl heptalene-4,5-dicarboxylates, when treated with 4 mol-equiv. of lithiated N,N-dialkylamino methyl sulfones or methyl phenyl sulfone, followed by 4 mol-equiv. of BuLi in THF in the temperature range of - 78 to 20°, give rise to the formation of 3-[(N,N-dialkylamino)sulfonyl]- or 3-(phenylsulfonyl)benzo[a]heptalene-2,4-diols (cf. Scheme 4, and Tables 2 and 3). Accompanying products are 2,4-bis{[(N,N-dialkylamino)sulfonyl]methyl}- or 2,4-bis[(phenylsulfonyl)methyl]-4,10a-dihydro-3H-heptaleno[1,10-bc]furan-3- carboxylates as mixtures of diastereoisomers (cf. Scheme 4, and Tables 2 and 3) which are the result of a Michael addition reaction of the lithiated methyl sulfones at C(3) of the heptalene-4,5-dicarboxylates, followed by (sulfonyl)methylation of the methoxycarbonyl group at C(5) and cyclization (cf. Scheme 5). It is assumed that the benzo[a]heptalene formation is due to (sulfonyl)methylation of both methoxycarbonyl groups of the heptalene4,5-dicarboxylates (cf. Schemes 6 and 8). The resulting bis-enolates 35 are deprotonated further. The thus formed tris-anions 36 can then cyclize to corresponding tris-anions 37 of cyclopenta[d]heptalenes which, after loss of N,N-dialkylamido sulfite or phenyl sulfinate, undergo a ring-enlargement reaction by 1,2-C migration finally leading to the observed benzo[a]heptalenes (cf. Schemes 8 and 9). The structures of the new product types have been finally established by X-ray crystal-structure analyses (cf. Figs. 1 and 2 as well as Exper. Part).
