Organométalliques allyliques siliciés: obtention et comportement

The Homoaldol Reaction, or How to Overcome Problems of Regio‐ and Stereo‐selectivity

“…58 [34] 59 [ b ] [54] 60 [ a ] [55] 61 [ a ] [36,56] [32,33,52,53,83] Propionic ucid-d3-reugents: 0 [58,59] 65 [ a -d ] [60,61] 66 [a,b] 1,l-Bisheterosubstituted allyl anions 45 (Y = e.g. phosphoryl, groups derived therefrom, and also CN, Scheme 6) are more direct, although not always more useful preparative solutions, because an acid, 47, is directly obtained by hydrolysis of the y-adducts 46 (Scheme 5).…”

3‐Silanyl‐propenylphosphonates: Properties and alkylation potential

“…Carbanions generated from allylphosphonates [ 11 or from allylsilanes [2] have been used for the preparation of dienes and polyenes via olefination reactions with electrophiles like aldehydes or ketones [3,4]. From the regioselectivity point of view, the condensation reactions occur usually exclusively at the carbon a to a heteroatom; however, in cases of bulkier electrophiles, the isomeric y product may become favored (Scheme 1).…”

Regio- and Stereo-selective Reaction of Chiral Alkoxy- and Aminomethyl-substituted α-Silylallyl Carbanions with Aldehydes

“…On the other hand, the g-products are a mixture of E-and Z-isomers (Table 1, Scheme 1). The Z-con®guration of the double bond formed was proved by 1 H NMR: a double triplet at d 5.6 and a doublet at d 5.3 with J 15.4, while the E-con®guration was shown by a double triplet at d 6.05 and a doublet at d 5.73. As Chan and Labrecque 8 have demonstrated, the a-silylallyl anion can exist as three species: exo-17, endo-18 and an open form 19.…”

“…a-Silylallyl carbanons 1 have been used extensively as synthetic intermediates, since the silyl group can be subsequently transformed to other electrophile equivalents thus enhancing its usefulness in synthesis. 2 When the carbanions are allylic in nature, the reactions of silylallyl anion 1 with various electrophiles can occur at either the a-or the g-position giving the a-product 2 or the g-product 3 respectively.…”

“…4 The reactions of chiral allylalkoxysilanes 4a±c in the presence of Lewis base, Schlosser's base (Bu n Li±Bu t OK) 5 or lithium diisopropylamide (LDA), generated the anions 10a±c, which reacted with aldehydes giving g-(E) products 11±13 exclusively in high yield (Table 1, Scheme 1). The E-con®guration of the double bond formed was deduced by 1 H NMR: a double triplet at d 6.2 and a doublet at d 5.7 with J 18.2. It is interesting that the high g-regioselection 6 in the reactions of alkoxy-substituted a-silylallyl anion 10a±c with aldehydes contrasts the favorable a-regioselection for halides under the same Lewis base conditions.…”