In alkene synthesis

General.—The relatively unreactive diethyl arylmethylphosphonates have been used quite successfully in alkene synthesis with phase-transfer catalysis.100 In a comparative study it was shown that anions derived from /S-ketophosphonamides (109) have very low reactivity whereas those from 0-ketophosphonates (110) react quite well with aldehydes to give frwjj-alkenes.101 Benzyl dimethyl phosphonoacetate (111) can be used to form alkenes, e.g. (112), from which the benzyl group can be removed by hydrogenolysis without disturbing the C=C bond.102 The carbanions (113) can be... 

Among those phosphonates used successfully in alkene synthesis with aromatic aldehydes were (114),106 (115),107 (116),108(117),109 and(118).110 The stereochemical... 

We have mentioned previously (see Section 3.1) the easy formation of a double bond by sulfoxide pyrolysis. Associated with an alkylative step of a metallated sulfoxide, the sequence is of great value in alkene synthesis [44U, 441], as in the one-pot reaction given here. 

Reviews have featured epoxidation, cyclopropanation, aziridination, olefination, and rearrangement reactions of asymmetric ylides 66 non-phosphorus stabilized carbanions in alkene synthesis 67 phosphorus ylides and related compounds 68 the Wittig reaction 69,70 and [2,3]-Wittig rearrangement of a-phosphonylated sulfonium and ammonium ylides.71 Reactions of carbanions with electrophilic reagents, including alkylation and Wittig-Homer olefination reactions, have been discussed with reference to Hammett per correlations.72... 

Even the ease of retrieval or possible photocatalytic uses or such in alkene synthesis from the carbonyl compounds principal in biochemistry (McMurry reaction) apparently cannot compensate for this as Ti is unable to bind the primary substrate. Eor Al, Zr or Ti abundance cannot replace catalytic versatility with respect to various functions, that is... 

As mentioned before, allenes can be formed by prototropic rearrangement of alkynes or, if an appropriate hydrogen is present in the allylic position, by direct elimination. The bromovinyl ether yields, in a trans elimination, the alkyne ether (Scheme 39), but the other isomer, where trans elimination is not possible, gives both the alkynyl ether and the allenyl ether (Scheme 40). This corresponds to the problem of Hofmann and Zaitsev orientation in alkene synthesis. 

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