Boronate fragmentation

Entry 8 was used to create the central nine-membered ring system found in the diterpene jatrophatrione. Entry 9 is an example of a boronate fragmentation (see p. 899). Entry 10 illustrates enolate fragmentation. The reaction presumably proceeds... 

Marshall boronate fragmentation is a variation of the Grob fragmentation (page 273) category. 

The stereoelectronic bond orientations are critical to the success of these reactions. This is easily seen in a generic Marshall Boronate Fragmentation. 

There are relatively few examples of formation of boron-carbon bonds in compounds containing preformed boron-boron fragments. The preparation of dibutylbis(dimethylamino)diborane(4) by alkyl-amino exchange has been noted (77). 

Reviews.—Recent reviews involving olefin chemistry include olefin reactions catalysed by transition-metal compounds, transition-metal complexes of olefins and acetylenes, transition-metal-catalysed homogeneous olefin disproportionation, rhodium(i)-catalysed isomerization of linear butenes, catalytic olefin disproportionation, the syn and anti steric course in bi-molecular olefin-forming eliminations, isotope-elfect studies of elimination reactions, chloro-olefinannelation, Friedel-Crafts acylation of alkenes, diene synthesis by boronate fragmentation, reaction of electron-rich olefins with proton-active compounds, stereoselectivity of carbene intermediates in cycloaddition to olefins, hydrocarbon separations using silver(i) systems, oxidation of olefins with mercuric salts, olefin oxidation and related reactions with Group VIII noble-metal compounds, epoxidation of olefins... 

Cf. Grob fragmentation. In fact, Marshall boronate fragmentation belongs to the Grob fragmentation category. 

Danishefsky has reported the total synthesis of epothilone 490 (129) via an intramolecular Suzuki macrocyclization of alkenyl boronic ester 130 bearing a terminal alkenyl iodide group [104]. The corresponding alkenyl boronate fragment was prepared by alkenyl boronate cross-metathesis as reported by Grubbs (Scheme 3.69) [105,106]. 

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