Aromatic formyl groups

Adjacent formyl groups facilitate the hydrolysis of certain aromatic esters, as illustrated by the examples below. Indicate a mechanism for this rate enhancement. ... 

The classical Vilsmeier-Haack reaction is one of the most useful general synthetic methods employed for the formylation of various electron rich aromatic, aliphatic and heteroaromatic substrates. However, the scope of the reaction is not restricted to aromatic formylation and the use of the Vilsmeier-Haack reagent provides a facile entry into a large number of heterocyclic systems. In 1978, the group of Meth-Cohn demonstrated a practically simple procedure in which acetanilide 3 (R = H) was efficiently converted into 2-chloro-3-quinolinecarboxaldehyde 4 (R = H) in 68% yield. This type of quinoline synthesis was termed the Vilsmeier Approach by Meth-Cohn. ... 

The applicability of the Gattermann synthesis is limited to electron-rich aromatic substrates, such as phenols and phenolic ethers. The introduction of the formyl group occurs preferentially para to the activating substituent (compare Friedel-Crafts acylation). If the /jara-position is already substituted, then the ort/zo-derivative will be formed. 

Electrochemically generated nickel is very selective for the reduction of aromatic nitro compounds into anilines, in which alkenyl, alkynyl, halo, cyano, formyl, and benzyloxy groups are not affected.84 Sodium sulfide has been used for the selective reduction of aromatic nitro group in the presence of aliphatic nitro groups (Eq. 6.44).85... 

By contrast with the reconcilable data observed with para-substituted substrates, a range of ortho substituents (entries h-j, Table 2.1) all resulted in significant weakening of the C7-C8 anti selectivity. We take these data to suggest that ortho substitution results in some steric inhibition of the rotamer in which the faces of the aromatic ring and formyl group are parallel (see structure III). 

In 1996, Wu et al. reported the isolation of murrayamine-M (162), a formyl analog of bicyclomahanimbicine (161) from the leaves of M. euchrestifolia collected in November in Taiwan. The UV spectrum Umax 243, 254 (sh), 292, and 325 nm] of murrayamine-M (162) indicated a 3-formylcarbazole. This assignment was supported by the IR spectrum [Vmax 1605 (aromatic system), 1675 (CHO), and 3300 (NH) cm J. The H-NMR spectrum resembled that of bicyclomahanimbicine (161), but exhibited a formyl group ( 10.08) at C-3 instead of the aromatic methyl group. The deshielded mete-coupled (/=1.7Hz) H-4 at 6 8.48 confirmed the position of the formyl group at C-3. Based on the spectral data, structure 162 was assigned to murrayamine-M (Scheme 2.32). The absolute configuration of 162 is not known (130). 

As well as the Bingel reaction and its modifications some more reactions that involve the addition-elimination mechanism have been discovered. 1,2-Methano-[60]fullerenes are obtainable in good yields by reaction with phosphorus- [44] or sulfur-ylides [45,46] or by fluorine-ion-mediated reaction with silylated nucleophiles [47]. The reaction with ylides requires stabilized sulfur or phosphorus ylides (Scheme 3.9). As well as representing a new route to l,2-methano[60]fullerenes, the synthesis of methanofullerenes with a formyl group at the bridgehead-carbon is possible. This formyl-group can be easily transformed into imines with various aromatic amines. 

Torok and co-workers312 have reported the one-pot synthesis of /V-arylsulfonyl heterocycles through the reaction of primary aromatic sulfonamides with 2,5-dimethoxytetrahydrofuran. When triflic acid is used in catalytic amount, IV-arylsulfonylpyrroles are formed (Scheme 5.34). Equimolar amount of triflic acid results in the formation of N- ary I s u I fo n y I i n do I e s, whereas /V-arylsu Ifonylcar-bazoles are isolated in excess acid (Scheme 5.34). In the reaction sequence 1,4-butanedial formed in situ from 2,5-dimethoxytetrahydrofurane reacts with the sulfonamide to give the pyrrole derivative (Paal-Knorr synthesis). Subsequently, one of the formyl groups of 1,4-butanal alkylates the pyrrole ring followed by a second, intramolecular alkylation (cyclialkylation) step. 

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