Wittig condensation extension

Other alternatives for chain extension have been developed. Wittig condensation between the dialdose derivative 194 and the (PPI13I) monosaccharide derivative 195 occurs with complete stereoselectivity, forming a cis linkage. Compound 196 is the precursor of a deaminotunicamine derivative.399... 

Seebach completed the first synthesis of optically active 9 as depicted in Scheme 4.2. ° Protected alcohol 10, available from an optically active p-hydroxy butyric ester, was alkylated with 2-lithio-1,3-dithiane. Deprotonation of this material followed by formylation with DMF then afforded 11. Chain extension to the unsaturated ester was accomplished via a Wittig condensation and deprotection to produce the monomeric unit 12 in 57% overall yield from 10. Double lactonization under Mitsunobu conditions (DEAD-PhjP) afforded a 60%... 

Synthesis of the carotenoid backbone by Wittig condensation between C(ll)/C(12), or C(H )/C(12 ) has been used most extensively. Apart from special cases, which will be discussed later, generally a C(1 l)-phosphonium salt is linked to a C( 12)-aldehyde (synthesis strategy 2). 

The functionalized carbocycle (8) has been prepared from D-glucose (carbon atoms numbered) by Wittig chain extension and intramolecular aldol condensation, lo... 

Good Z-selectivities were observed for the reaction of aldehydes with carboxy ylides prepared from the corresponding phosphonium salt and LHMDS. This strategy has been extensively used in the total synthesis of prostaglandins, monohydroxy-eicosatetraenoic acids (HETE), and leukotrienes. Eor instance, the Wittig condensation between aldehyde 5 and car-boxy phosphonium salt 6 in the presence of LHMDS provided 49% yield of the TBDPS-protected 10(5)-HETE methyl ester 7 (eq42). ... 

Wittig or Wittig-Horner condensation between substituted terephthalaldehydes and p-xylene-diylphosphonium salts is also extensively used in the preparation of alternating PPV copolymers, e.g., containing different substituents in adjacent phenylene units (Scheme 2.8) [48]. 

These amidines have been extensively applied to dehydrohalogenation in organic synthesis and in some cases DBU (1) is more effective than DBN (2) [5]. A double bond can be also introduced into organic molecules by elimination of sulfonate ester instead of the halogen atom (i.e. dehydrosulfonation in addition to dehydrohalogenation). Furthermore, these amidines can be applied to the Wittig reaction [6], aldol condensation [6], 1,3-allyl rearrangement [7] and epimerization of the (3-lactam skeleton (at Ce of the penicillic acid derivatives). Sterically hindered phenols (e.g. 2,6-di(ferf-butyl)-4-fluorophenol) are (9-acetylated with DBU (1), which is superior to sodium hydroxide in the synthesis [8]. 

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