2- -2-alkenoic acid alkanal

By this method (Z)-monounsaturated fatty acids and esters could be obtained with an ( )-isomer content of less than 10% this stereoselectivity being however inferior to that of the commonly used acetylenic approach 55,56). However, the salt-free techniques used today in Wittig reactions allow (Z)-alkenoic acids to be synthesized with less than 2% of the ( )-isomers. Thus, Bestmann et al. prepared methyl and ethyl esters of (Z)-4,5,6,7,8,9,ll- and 13-alkenoic acids of different chain lengths 35,57 62), which served as intermediates in the synthesis of insect pheromones, both by reaction of co-alkoxycarbonyl-substituted alkyl-triphenyl-phosphonium salts with simple alkanals and of co-formylalkanoic esters with alkylidenephosphoranes. As the starting material for the synthesis of -substituted alkyl-phosphonium salts co-chloro- and -bromocarboxylic esters were used. The corresponding -substituted aldehydes can usually be obtained by ozone cleavage of suitable olefin derivatives or by oxidation of alkohols 57,58). 

Alkenoic acids are formed by heating of oils and fats of animal or plant origin. They can also be prepared by hydrolysis of the corresponding esters158). The Wittig reaction of alkanals 215 with alkoxycarbonylmethylene-triphenylphos-phorane 217 affords the ( )-2-alkenoic esters 218 in about 95 % yield of the ( )-isomer. Alkaline hydrolysis of the esters 218 gives the ( )-2-alkenoic acids 220 (Scheme 41). 

Fragmentation of a l-silyloxybicyclo[/i.l.O]alkane with Pb(OAc)4 in acetic acid leads to two-bond cleavage to yield an alkenoic acid (Scheme 9). The reaction involves fission of the two bonds connected to the carbon bearing a silyloxy group. The reaction is considered to involve prior conversion of the silyloxycyclopropane to the corresponding cyclopropanol. In fact, treatment of a silyloxycyclopro-pane under strictly aprotic conditions gives a product due to one-bond cleavage (Scheme 9). 

Many Pseudomonas strains accumulate MCL-PHAs from alkane, alkene, al-kanoate, alkenoate, or alkanol [5,6,14,96]. The composition of the PHAs formed by the pseudomonads of the rRNA homology group I is directly related to the structure of the carbon substrate used [6]. These results suggested that MCL-PHAs are synthesized from the intermediates of the fatty acid oxidation pathway. In almost all pseudomonads belonging to the rRNA homology group I except Pseudomonas oleovorans, MCL-PHA can also be synthesized from acetyl-CoA through de novo fatty acid synthetic pathway [97]. The -oxidation pathway and de novo fatty acid synthetic pathway function independently in PHA biosynthesis. 

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