Arene-1,2-dialdehydes

A two-step synthesis of arenediynes from arene-1,2-dialdehydes has been reported (Scheme 15). Dibromomethylenation of dialdehydes under Corey-Fuchs conditions provides the tetrabromides, which on treatment with n-BuLi or LDA afford 3,4-unsaturated 1,5-diynes, the key structural moiety present in several naturally occurring... 

The Knoevenagel reaction is a base-catalyzed condensation between a dialdehyde and an arene possessing two sites with relatively acidic protons. In this polymerization, shown schematically in Scheme 34, deprotonation affords a difunctional nucleophile that subsequently attacks the carbonyl functionalities present in the other monomers. Elimination is the final step in the Knoevenagel sequence, and the use of monomers with highly acidic protons drives the reaction to completion. A number of research groups have employed this method to obtain PPV and its substituted analogs 29 [126,140-146]. 

In analogy to intermolecular pinacolic coupling reactions, organometallic dialdehydes have served as precursors for the intramolecular version of the reaction, affording cyclic 1,2-diols [39]. Both arene chromium tricarbonyl (Eq. 29) and ferrocene complexes (Eq. 30) afford excellent yields of the desired products. 

A head to head double calix[4]arene system linked at the 1 -distal upper rim positions of tetrapropyloxy calix[4]arene with 2,6-diamino-pyridine groups was obtained by condensation of l,3-diaminocalix[4]-arene with pyridine dialdehyde and showed binding abihty toward viologen type guest molecules (2002T9019). 

We have previously described the synthesis of calixcrowns by one-pot reactions. In a different approach the calix(aza)crowns were constructed by stepwise synthesis. The synthesis began with the condensation of cone-1,3-dialdehyde derivative 16 with various primary diamines to afford Schiff base-p-terr-butylcalix[4]arenes 17-20 in the cone conformation [29, 30]. Hydrogenation of 18 and 19 with NaBHt produced chlorohydrates 21HC1 and 22-HCl and subsequent deprotonation with NaOH lead to the di-aza-benzo-crown-ether-/j-tert-butylcalix[4]arenes 21 and 22 in almost quantitative yield [31] (Figure 6). 

Synthesis of Arene Oxides. Reaction of (Me2N)3P with aromatic dialdehydes provides arene oxides such as benz[a]anthracene 5,6-oxide (2a) (eq 5). These compounds, also known as oxiranes, are relatively reactive, undergoing thermal and acid-catalyzed rearrangement to phenols and facile hydrolysis to dihydrodiols. Consequently, their preparation and purification requires mild reagents and condition.s. The importance of this is underlined by successful synthesis of the reactive arene oxide (2b) in 75% yield using appropriate care, despite a previous report of failure of the method. While compound (2b) is a relatively potent mutagen, it is rapidly detoxified by mammalian cells. The principal limitation of the method is the unavailability of the dialdehyde precursors, which are obtained through oxidation of the parent hydrocarbons, e.g. by ozonolysis. 

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