Wittig salt

Dietary /1-carotene, a nutritionally important source of vitamin A, exhibits a protective effect against cancer risk31,32. The deuteriated compound, 10,10, 19,19,19,19, 19, 19 -2H8-/S-carotene, 32, has been obtained33 by double condensation of the C-15 Wittig salt 33 with the symmetrical C10 dial 2,7-dimethyl-2,4,6-octatrienedial, 34 (equation 13) for the study of /J-carotene metabolism in humans. 

Next again a Wittig reaction succeeds. Aldehyde 55 is directly converted to a 3 1 mixture of E- and Z-enynes 16 upon exposure to the in situ generated Wittig salt 15. The E-isomer is built as main product, passing the anti-configurated oxaphosphetane 56. 

Although the Smith second-generation synthesis offered several improvements over their initial route, the use of the ultrahigh pressure over extended time periods in the formation of the key Wittig salt 49 severely limited the possibility of further... 

This revised strategy demonstrates that a simple change in hydroxyl protecting groups can markedly influence reactivity and selectivity. While formation of the Wittig salt 51 could now be achieved at atmospheric pressure, its coupling with aldehyde 45 only proceeded in moderate yield and selectivity. 

The initial retrosynthetic analysis for a route to travoprost, using the Newton-Roberts route, provided three key synthons a) the a-chain was derived from the commercially available Wittig salt, (4-carboxybutyl)triphenylphosphonium bromide b) the co-chain required a route to the single enantiomer mixed cuprate reagent, most conveniently derived from the propargylic alcohol via the trans-vinyl iodide, to be developed and c) the cyclopentane core could be derived from the single enantiomer protected bromohydrin (Figure 30.3).llc 25... 

Dinor-/3,)3-carotene has been synthesized. Nor-safranal (61) was prepared in four steps from 4-hydroxy-2,5,5-trimethylcyclopent-2-en-l-one (62) and reduced to nor-/3-cyclocitral (63). With the Grignard reagent (64) this gave the alcohol (65) and thence the Wittig salt (66) which was condensed with the C14 dial (67) to give the dinor-/3-carotene (68). 

Two methods of end-group construction were used in the synthesis of methyl azafrin [methyl 5,6-dihydroxy-5,6-dihydro-10 -apo-/3-caroten-10 -oate (72)]. The first route used the epoxy-intermediate (73) which on treatment with acid gave the 5,6-diol (74). In the second procedure the trimethylcyclohexanone (75) was converted into the hydroxy-ketone (76) which reacted with the Cg fragment (77) to give the acetylenic compound (78). The Wittig salt (79) was made from either (74) or (78) and used in the condensation to form methyl azafrin. 

In a synthesis of all-tran5-retinonitrile (108) the Cio aldehyde (109) was converted via the oxime into the nitrile (110). Oxidation of this gave the aldehyde (111) which with the j8-cyclogeranyl Wittig salt (112) afforded retinonitrile in... 

In the third step, the phosphonium salt and / -BuLi form a Wittig salt in situ. In the subsequent reaction, PhsP O is obtained as one of the products. 

The final step provides the desired Wittig salt. 

Several other carotenoids have been synthesized by standard routes involving condensation of Wittig salts with the Cio and C20 dials (46) and (47). Thus the Wittig salts (48), (49), and (50) were used to prepare the acyclic 1,2-dihydrocarotenes... 

Wittig salt (51). Wittig reaction with the C14 dialdehyde (52) gave racemic (27). The 3-hydroxy-p-ring system was also obtained from a-ionone (53). Oxidation with t-butyl chromate gave the ketone (54), which with ethanediol underwent double-bond migration to give (55), which was hydrolysed in the presence of... 

Many retinaldehyde, retinol, and retinoic acid derivatives and analogues have been synthesized. The (3i )-3-hydroxy-derivatives (98), (99), and (100) were prepared from the optically active C15 Wittig salt (31).68 9-Bromoretinaldehyde (101 trans and 9-cis), 13-bromoretinaIdehyde (102 trans and ll-cis), phenyl-retinaldehyde (103 trans and 9-cis), and p-dimethylami nophenyl retinaldehyde (104 trans) have been prepared and used to make bacteriorhodopsin analogues.69 5,6-Dihydroretinaldehyde (105) and its desmethyl analogue (106) also formed... 

Dtittmann, H., and Weyerstahl. P.. ], 3-Butadiene-2-carboxylic acids starting from the Wittig salt of 2-(bromomethyl)acrylic acid. Chem. Ber., 112, 3480, 1979. 

A total synthesis of LTB has been reported by Corey et al. as outlined in Scheme 3.16. By using the Sharpless asymmetric oxidation, the enantiomer of the epoxy alcohol in Scheme 3.11 was obtained, from which the corresponding aldehyde was then prepared. The epoxy olefin was transformed to the desired Wittig salt 39, which was condensed with the homologated aldehyde 40, giving a modest yield of the desired (8Z)-isomer. Again, the benzoyloxy aldehyde... 

The synthesis of a number of 2,2 -dinor-carotenoids has been described." Wittig reaction between the Cio dial (52) and the appropriate Wittig salt (70)... 

A new approach to the 0-functionalisation of enones involves treating the substrate with t-butyldimethylsilyl triflate (TBDMSOTf) in the presence of triphenylphosphine. This phosphoniosilylation reaction gives a silylenol ether-wittig salt which, after lid formation, may be condensed with an aldehyde to give a silyl dienol ether. These may either be protiodesilylated to give the 0-functionalised enone or alternatively used in aldol... 

The synthesis of a gas-generating composition starts with the synthesis of a poly(vinyltriazole). A substituted triazole salt is added to a free radical brominating reagent, such as A-bromo succinimide, and to a radical initiator to form a brominated triazole. The brominated triazole is then added to triphenylphosphine to form a Wittig salt. Formaldehyde in alkaline medium effects the formation of a vinyltriazole salt, which can be polymerized with AIBN and a catalytic amount of a cationic initiator or a Ziegler-Natta catalyst. The reaction sequence is shown in Figure 9.10. 

A stereoselective synthesis of 5(5),6(7 ),15(5)-trihydroxy-20 4(7 ,9 ,l 1Z,13 ) from D-xylose using zinc-mediated deoxygenation of the 4-hydroxy-2-butenoic acid moiety and base- induced double elimination of 4,5-epoxy allyl chloride as key steps was reported (44). The enantiomers R)- and (5)-3-hydroxy-20 4(5Z,8Z,llZ,14Z) were synthesized from coupling of a chiral aldehyde intermediate with a Wittig salt, which were derived from 2-deoxy-D-ribose and arachidonic acid, respectively (45). 

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