1,2-Metalate rearrangement

The western part 97 of tylosin a ycon (96) a 16-membered macrolide has also been sj nthesized using this Kocienski metalate rearrangement [66]. Treatment of the lithiated dihydrofuran 99 with the stannyl cuprate [67] obtained from BusSnLi and CuCN followed by Mel alkylation exclusively gave the vinyl stan-nane 100 in 80% yield. In the last stage stannyl cupration [68] of the deprotected enyne diol 101 afforded the desired ( , ) stannyl diene 97 in 85% yield. 

The advantage of this strategj is thus the subsequent trapping of the metalate rearrangement product to provide a dean efficient and highly stereosdective route to the trisub stitued alkenes. 

The carbocupration of alkynes occurs in a ds fashion to afford the sj nthetically useful CIS alkenyl products. RecenfLy copper-mediated introduction of heteroatoms sudi as stannyl and silyl groups has become frequently used in place of introduction of carbon units as an efficient strategy to build important precursors in syn- 

As described above many copper-mediated reactions play important roles in the syntheses of natural and unnatural products. To date natural product syntheses using organocopper reagents have been accomplisheds and will undoubtedly be increasing greatiy from now on. 

Normant, Syn-theds 1972, 63—80 G. H. PosInter, An Introduction to Synthesis Using Organocopper Reagents, Wiley, New York, 1980 E. Erdiic, Tetrahedron 1984, 40, 641-657 R. J. K. Taylor, Synthesis 1985, 364-392  

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The reduction of alkyl-substituted siUcon and tin peroxides with sodium sulfite and triphenylphosphine has been reported (33,93). Alkyl-substituted aluminum, boron, cadmium, germanium, siUcon, and tin peroxides undergo oxygen-to-metal rearrangements (33,43,94), eg, equations 22 and 23. 

Scli ir 3.33. Metalate rearrangement of a mixed i/inyl(ctannyl)cijprate derived from a ZJ-dikiydrofijran (TIPS = triicopropylcilyl) [llSb. ... 

An alternative explanation is that the regioselectivity of insertion (180 vs. 181) is determined by the rate of 1,2-metallate rearrangement, the formation of the regioisomeric ate complexes 176 and 177 being fast and reversible (Scheme 3.39). Interconversion of 176... 

Applications of organocopper reagents and reactions to natural product synthesis are classified by reaction type conjugate addition, Sn2 substitution, Sn2 substitution, 1,2-metalate rearrangement, and carbocupration. 

A 1,2-metalate rearrangement of a higher order cuprate, known as a Kodenski rearrangement [64], was used as a key step in the synthesis of the marine antiinflammatory sesterterpenoid manoalide 95 (Scheme 9.20) [65]. Treatment of the alkenyl lithium 89 (prepared from the alkenylstannane 88 with s-BuLi in a diethyl ether-pentane mixture) with the homocuprate 91 (produced from iodoalkane 90) gave the iodoalkene 94 in 72% overall yield from 88. The reaction proceeds as fol-... 

These reactions involve metallate rearrangements , migratory insertion and transition metal-catalysed vinylic substitution reactions. They also perform well in applications in natural product synthesis . Many useful synthetic possibilities arise from application of ring-closing olefin metathesis (RCM) to unsaturated homoaldol products and their derivatives by means of the Grubbs catalyst 3942 4-286 Equation 105 presents some examples. ... 

Only one example of electrophilic behavior of silicon-stabilized lithiooxiranes is reported. Intermolecular C—Li insertion followed by Li20 elimination occurs by raising the temperature, and ( ) vinylsilanes are obtained stereoselectively (Scheme 80). Reaction of lithiooxiranes with aluminum , zirconium and silicon reagents leads to the corresponding ate complexes, which undergo 1,2-metallate rearrangements. 

In contrast to the examples reported above, some other aryl- and vinyl-stabilized lithiooxiranes show a strong electrophilic behavior and undergo rearrangement reactions (Scheme 83, see also Section V.A.2.a for other examples). Lithiated styrene oxide has been engaged in 1,2-metallate rearrangement with zirconacycles . 

METALLATE REARRANGEMENT (Z)-4-(2-PROPENYL)-3-OCTEN-1 -OL [3-Octen-1-ol, 4-(2-propenyl)-, (Z)-]... 

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