Enolates regio-defined

The introduction of asymmetry in conjugate additions can be promoted by chiral acceptors. The preparation of regio-defined magnesium enolates from copper(I)-mediated conjugate addition of Grignard reagents has been extensively used in many important... 

The inconveniences associated with these procedures are more than offset by their ability to introduce stereo- and regio-defined alkenyl groups in a completely regio-controlled manner. Recent results indicate that this methodology is also applicable to a-substitution with alkyl, alkynyl, and other carbon groups [136]. Collectively, it promises to supplement significantly the current scope of the enolate substitution methodology. This method is also... 

FORMATION AND ALDOL REACTIONS OF REGIO-DEFINED ENOLATES... 

The introduction of the foregoing bases opened the way for the preparation of structurally defined enolates examples are seen in equations (5) to (7). The first examples of the use of these regio-defined enolates in crossed aldol reactions were reported by Stork, Kraus and Garcia in 1974 representative examples are shown in equations (8) and (9). ... 

Heng and Smith found that the regio-defined enolates resulting from conjugate addition of lithium di-alkylcuprates to enones undergo acceptable aldol additions under the House conditions. One of the... 

The great power of the aldol addition reaction lies in the ability to generate and use structurally defined enolates. In this section, the emphasis is on the formation of regio-defined enolates, and the aldol reactions of these enolates. Stereochemical issues are dealt with in Sections 1.6.2-1.6.4. 

A classic method for generating regio-defined enolates is metal-ammonia reduction of an enone.26 Stork and d Angelo found that the enolate resulting from lithium-ammonia-r-butyl alcohol reduction of octalone (3), followed by evaporation of ammonia, suspension of the enolate in ether and treatment with... 

Decadiene and cyclohexenyl triflate added to a soln. of dimethyl sodiomalonate (generated from dimethyl malonate and NaH), ca. 2 eqs. LiCl, and a little Pd(PPh3)4 (freshly generated) in DMSO, and heated under argon at 65° for 48 h - product. Y 80% (90% E). Regio-defined enol triflates are more readily accessible than vinyl halides (cf. 40, 584). F.e.s. B. Friess et al.. Tetrahedron Letters 29, 4089-92 (1988). 

The significant synthetic advantage of this approach is the isolation of regio-and stereo-defined enol silyl ethers of optically active y-nitro aldehydes (Table 4.2). For example, after the reaction of 16a with trans-cinnamaldehyde, the resulting mixture can be directly purified by silica gel column chromatography to produce the optically active enol silyl ether 20a in 90% yield (Table 4.2, entry 1). High... 

Startg. vinyl bromide treated with 1 eq.. sec-butyllithium in THE at —78, and oxidized with bis(trimethylsilyl) peroxide after 15 min product. Y 75%. The method permits the generation of ketone enolates in a regio- and stereo-defined manner, and is especially useful for ketone derivs. where the two a-sites are similar. F.e.s. F.A. Davis et al., Tetrahedron Letters, 29, 4269-72 (1988) f.e.s. L. Camici et al., Tetrahedron 44, 4197-206 (1988). 

Reductive generation of regio- and stereo-defined enolates C... 

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