Dichloromethane , polyene

When dichloromethane (DCM) solutions of the polyenes which had been prepared as described (39) were added to DCM solutions of TFA new species were formed which had strong absorptions in the region 500-850 nm. Figure 6 shows seme typical spectra for such a solution, (a) immediately after mixing, (b) after a further 20 minutes and (c) after 200 minutes. In spectrum (a) clearly defined maxima are visible at 590, 660, 730 and 790 nm the intensities of which change with time in a way which indicates that they are inter-related (figure 7). As Arg0 decreases,... 

Alkoxy-a,/S-unsaturated aldehydes 201 could be converted into the corresponding polyenals 202 in the presence of DBU and molecular sieves 3A or 4A in benzene, tetrahydrofuran, acetonitrile, or dichloromethane at... 

TABLE 5. Observed absorption maxima (Amax) of all-tra 5-cc,fi)-dithienyl-polyenes in dichloromethane ... 

The synthesis of these isomers was guided by a strategy of using only stereochemically pure phosphonium salts and polyene aldehydes as intermediates. To show the importance of various chromatographic and spectroscopic methods for the analysis of such intermediates, the preparation of the (7Z)-isomer of lycopene (31), is briefly considered in Scheme 5. This isomer is a major component of the mixture of (all- )-, (7Z)- and (7Z,7 Z)-lycopene formed in the Wittig reaction of geranyltriphenylphosphonium bromide with crocetindialdehyde [10] in the presence of NaOMe in dichloromethane [18]. 

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