Marshall boronate fragmentation

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. 

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

The past few years have witnessed a considerable effort by several research groups to effect stereoselective syntheses of appropriately substituted hydroazulenes. Recently some new approaches to this problem have been reported. Marshall and Huffman, for instance, have found that treatment of the enone-mesylate (395) with diborane followed by base-induced fragmentation of the intermediate boronate (396) yielded the cyclodecadienol (397) in 60 % yield. Solvolysis of the p-nitrobenzoate of (397) in aqueous dioxan containing sodium bicarbonate afforded the hydroazulenol (398) in 70 % yield. The high degree of stereoselectivity in this reaction is rationalized on the basis of the preferred mode of cyclization of the allylic cation (399). To date, the solvolytic routes to hydroazulenes have... 

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