Dipole aliphatic aldehydes

The reactions of l,3-thiazolium-4-olates with aliphatic aldehydes carried out in refluxing benzene or dichloromethane, have been reported to produce a series of highly functionalized (3-lactams and thiiranes at the same time [230]. The critical issue of the stereoselection was discussed in terms of the endo and exo approaches (respective to the aldehyde substituent) to any enantiotopic face of the heterocyclic dipole. Such orientations involved either the Re or the Si faces of the prochiral aldehydes (Scheme 105). 

Table XCIV, Dipole Moments of Aliphatic Aldehydes...

Part XXIII. The Dipole Moments of Some Aliphatic and Aromatic Aldehydes and of Anthrone. J. chem. Soc. (London) 1938, 1444. 

The synthesis of a new series of tetrahydro-oxazolo[4,5-d]-1,2,3-triazoles (102) has been reported. The triazolium imide 1,3-dipole (104) reacted with ( )-cinnamaldehyde in refluxing ethyl methyl ketone. It is significant that it was to the C=0 bond of the a,/ -unsaturated aldehyde that the cycloaddition took place, yet analogous addition to benzaldehyde or aliphatic ketones was not possible. The primary products of the cycloaddition reaction (105) underwent a sigmatropic rearrangement to furnish the new ring system (102) as shown in Scheme 23 <90JCS(P1)2527>. 

Derivatives of durene and mesitylene— In Chapter 9 it was pointed out that in derivatives of durene and mesitylene stcric factors due to the methyl groups may hinder the resonance of the substituent group with the ring system. In Tables Cl and C//the dipole moments of these compounds are compared with the corresponding aromatic and aliphatic derivatives. The dipole moments of the acetyl derivatives of durene and mesitylene are very similar to the value for acetone but lower than that for acetophenone, where resonance with the ring occurs. In aldehydes, on the other hand, where apparently there is no steric hindrance, the moment is almost identical with that of benzaldehyde. 

Sample compounds are better retained by the reversed-phase surface the less water soluble (i.e. the more nonpolar) they are. The retention decreases in the following order aliphatics > induced dipoles (e.g. CCI4) > permanent dipoles (e.g. CHCI3) > weak Lewis bases (ethers, aldehydes, ketones) > strong Lewis... 

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