Ylide reagents

Step 2 Oxidation with pyridinium chlorochromate (PCC) affords the aldehyde. Step 3 Wittig reaction provides the TM. (Note The ylide reagent is prepared by treating Ph3P with CD3I to obtain Ph3P+CD3 r and followed by deprotonation with w-BuLi.)... 

Asymmetric ylide reactions such as epoxidation, cyclopropanation, aziridination, [2,3]-sigmatropic rearrangement and alkenation can be carried out with chiral ylide (reagent-controlled asymmetric induction) or a chiral C=X compound (substrate-controlled asymmetric epoxidations). Non-racemic epoxides are significant intermediates in the synthesis of, for instance, pharmaceuticals and agrochemicals. 

Acylation has frequently been used to convert arsonium ylides into other more stabilized ylides, reagents used being acid chlorides ° acid anhyd-rides " or esters These examples all involve C-acylation but complications can arise, as shown in equation 17 It was suggested that reaction with benzoyl bromide gives a kinetically controlled product which, in the presence of acetate, is converted into the thermodynamically controlled product In this case delocalization of the negative charge leads to acylation at a site other than the ylidic carbon atom. 

Several groups have investigated the use of complex sulfur ylide reagents for a key carbon-carbon bond formation step in leukotriene synthesis (equation 4). For example, tetraene (6) reacted with methyl S-oxopentanoate to give an 8S% yield of the desired epoxides as a mixture of cis and trans isomers. Significantly, only small amounts of by-products resulting from elimination or rearrangement of the sulfonium salt were observed. 

Furan-2,5-dione, or maleic anhydride, can quite reasonably be regarded as furanoquinone, the reduced form being furan-2,5-diol. The carbonyl groups do have some ketonic activity, and in Scheme 23 the key step of a second route to freelingyne (86 in Vol. 30) makes use of this capacity in a reaction with another phosphorus ylide reagent.96 (cf. Scheme 16). Even ordinary (carbonyl stabilized) carbanions will undergo such aldol con-... 

Scheme 6 Reaction of naltrexone methyl ether (22) with a stable sulfur ylide. Reagents and conditions (a) trimethylsulfoxonium iodide, NaH, THF, 55 °C to rt, 67%...

Cyclopropanated 1,3-disubstituted 1,2-dihydropentalenes 12 were prepared from 1,2-di-hydropen talenes 11 by methylene transfer from trimethyloxosulfonium iodide in dimethyl sulfoxide using sodium hydride at room temperature. The phenyl substituent at Cl completely shields the ryn-side of the reactive C3 to C4 double bond against attack by the ylide reagent. Compounds 12 serve as starting materials for hexahydroindene derivatives by acid-catalyzed ring-expansion reactions. 

Scheme 11 indicates the usefulness of salts derived from Wittig ylide reagents and anhydrides of perfluorocarboxylic acids in the synthesis of fluorinated alkenylphosphonic diesters (127), often together with (epoxyalkyl)phosphonic diesters (128)(Rf = CF3 or... 

---