From Colchicine and Some of Its Derivatives to 1,2,3,9,10‐Pentamethoxybenzo[<i>a</i>]heptalenes

Kouroupis, Pavlos; Hansen, Hans‐Jürǵen

doi:10.1002/hlca.19950780517

Cited by 14 publications

(10 citation statements)

References 76 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We observed a similar shift effect of the heptalene absorption band in the CD spectra of 1,2,3,9,1O-pentamethoxybenzo[a]heptalene and its 4-methyl derivative [22]. The X-ray crystal-structure analysis of both compounds revealed an increase of the central heptalene gauche angles from at least 52 to 59", accompanied by a hypsochromic shift of the heptalene absorption band by 12 nm [22], i.e., the peri-positioned Me group at C(4) of the benzo[a]heptalene skeleton has a significant influence on the twisting of the heptalene skeleton. The Me substituent at C(4) of the benzo[a]heptalenes can be compared with the Me substituent at C(3) of 23a.…”

Section: ")supporting

confidence: 70%

“…There is no doubt on the absolute configuration of the new heptaleno[l,%-clfurans 6 and 23, since (-)-(P)-5a led, upon dehydrogenation with MnO,, to (-)-(P)-6a which exhibited a nearly identical CD spectrum as the faster-moving antipode of 6a on the Chiralcel OD column. Since the AE values of both (-)-6a samples were also identical, we can conclude that no racemization had occurred on the reaction paths of (-)-(P)-5a to ' I ) The antipodes of 1,2,3,9,10-pentamethoxybenzo[a]heptalenes show on the same analytical Chiralcel OD column with hexane/i-PrOH (85-95%/15-5%) as eluant a similar retention-time behavior, i.e., tR((+)-(M)forms)/tR((-)-(P)-forms) = 1.2-1.4 (cf: [22]). H-C(4) appears as broads due to 'J(Me-C(S),H-C(4)) = 2.…”

Section: ")mentioning

confidence: 99%

See 1 more Smart Citation

Formation of Heptaleno[1,2‐c]furans and Heptaleno[1,2‐c]furanones

Uebelhart

Mohler

Fallahpour

et al. 1995

Helvetica Chimica Acta

Self Cite

View full text Add to dashboard Cite

The dehydrogenation reaction of the heptalene-4,5-dimethanols 4a and 4d, which do not undergo the double-bond-shift (DBS) process at ambient temperature, with basic MnO, in CH,C1, at room temperature, leads to the formation of the corresponding heptaleno[l,2-c]furans 6a and 6d, respectively, as well as to the corresponding heptaleno[l,2-c]furan-3-ones 7a and 7d, respectively (cJ Scheme 2 and 8). The formation of both product types necessarily involves a DBS process (cf. Scheme 7). The dehydrogenation reaction of the DBS isomer of 4a, i.e., 5a, with MnO, in CH,CI, at room temperature results, in addition to 6a and 7a, in the formation of the heptaleno[l,2-c]-furan-Lone 8a and, in small amounts, of the heptalene-4,5-dicarbaldehyde 9a (cf. Scheme 3 ) . The benzo[a]heptalene-6,7-dimethanol4c with a fixed position of the C=C bonds of the heptalene skeleton, on dehydrogenation with MnO, in CH,Cl,, gives only the corresponding furanone l l b (Scheme 4). By [ZHz]-labelling of the methanol function at C(7), it could be shown that the furanone formation takes place at the stage of the corresponding lactol [3-'H2]-15b ( c t Scheme 6). Heptalene-1,2-dimethanols 4c and 4e, which are, at room temperature, in thermal equilibrium with their corresponding DBS forms 5c and 5e, respectively, are dehydrogenated by MnO, in CH2C12 to give the corresponding heptaleno[l,2-~]furans 6c and 6e as well as the heptaleno[l,2-c]furan-3-ones 7c and 7e and, again, in small amounts, the heptaleno[l,2-c]furan-l-ones 8c and Se, respectively (cf. Scheme 8). Therefore, it seems that the heptalene-1,2-dimethanols are responsible for the formation of the furan-l-ones (cf. Scheme 7). The methylenation of the furan-3-ones 7a and 7e with Tebbe's reagent leads to the formation of the 3-methyl-substituted heptaleno[l,2-c]furans 23a and 23e, respectively (cf. Scheme 9 ) . The heptaleno[l,2-c]furans 6a, 6d, and 23a can be resolved into their antipodes on a Chiralcel OD column. The (P)-configuration is assigned to the heptaleno[l,2-c]furans showing a negative Cotton effect at ca. 320 nm in the CD spectrum in hexane (cf. Figs. 3-5 as well as Table 7). The (P)-configuration of (-)-6a is correlated with the established (P)-configuration of the dimethanol (-)-5a via dehydrogenation with MnO,. The degree of twisting of the heptalene skeleton of 6 and 23 is determined by the Me-substitution pattern (cf. Table 9). The larger the heptalene gauche torsion angles are, the more hypsochromically shifted is the heptalene absorption band above 300 nm ( c j Table 7 and 8, as well as Figs. 6-9).

show abstract

Section: ")supporting

confidence: 70%

Section: ")mentioning

confidence: 99%

Formation of Heptaleno[1,2‐c]furans and Heptaleno[1,2‐c]furanones

Uebelhart

Mohler

Fallahpour

et al. 1995

Helvetica Chimica Acta

Self Cite

View full text Add to dashboard Cite

show abstract

“…Ketones react with trialkyloxonium salts to activate the carbonyl to produce vinyl ethers [59,60] or aromatic or conjugated cations, [61,62] or to increase the electrophilicity of the ketone for attack by various nucleophiles. [63,64] 37.6.2.3.3…”

Section: Variation 2: Ketone O-alkylationmentioning

confidence: 99%

Product Class 6: Oxonium Salts

Forsyth¹

2008

Category 5, Compounds With One Saturated Carbon Heteroatom Bond

View full text Add to dashboard Cite

“…-We have reported already in extenso on the UV/VIS and CD spectra of heptalenes [25] [26] and of some benzo[a]heptalenes [27] [28]. Here, we want to discuss the spectra of this latter class of compounds in more detail, especially with regard to the influence of the benzo fusion on the spectra.…”

Section: Uv/vis and CD Spectra Of Benzo[a]mentioning

confidence: 99%

Benzo[a]heptalenes from Heptaleno[1,2‐c]furans. Part 2

Uebelhart

Weymuth

Linden

et al. 2007

Helvetica Chimica Acta

View full text Add to dashboard Cite

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 ...

show abstract

From Colchicine and Some of Its Derivatives to 1,2,3,9,10‐Pentamethoxybenzo[a]heptalenes

Cited by 14 publications

References 76 publications

Formation of Heptaleno[1,2‐c]furans and Heptaleno[1,2‐c]furanones

Formation of Heptaleno[1,2‐c]furans and Heptaleno[1,2‐c]furanones

Product Class 6: Oxonium Salts

Benzo[a]heptalenes from Heptaleno[1,2‐c]furans. Part 2

Contact Info

Product

Resources

About