Brook rearrangement trimethylsilane

Recently, analogues of nucleosides [60], natural products Huperzine-A [61] and Hydroartemisinin [62], and inhibitors of metallo-/ -lactamases have been synthesised [63]. With acylsilane electrophiles, the initial adducts undergo Brook rearrangement which is interrupted by -Si bond fission with loss of fluoride anion (Eq. 16), leading to the formation of extremely useful difluoro-enol silanes [64]. Of the various fluoride sources employed, the tetrabutylam-monium triphenyldifluorostannate described by Gingras appears to be particularly effective. The numerous other methods for trifluoromethylation formed the subject of an exhaustive review [65]. More recently, the Olah group described a chlorodifluoromethyl trimethylsilane which is expected to have a rich chemistry [66]. 

In an interesting transformation, reaction of benzoyl trimethylsilane with lithium enolates derived from various methyl ketones gives rise to 1,2-cyclopropanediols, predominantly with the cis configuration, in good yields (Scheme 77). The reaction, which proceeds through addition, Brook rearrangement and cyclization, is also successful with a,/l-unsaturated acyl silanes vide infra, Section IV.D)187. 

The [4 + 2] cycloaddition of a-phenylselenopropenoyl trimethylsilane (75) with 2,3-dimethylbuta-1,3-diene is unusual in that a significant portion of product mixture consists of the hetero-Diels-Alder dihydropyran adduct 76. The phenylselenenyl substituent appears to be responsible for this unusual pattern of reactivity, since propenoyl trimethylsilane gives only the expected regioisomer (77, X = H) (Scheme 116)14. a-Selenenyl substituted a,/l-unsaturated acyl silanes such as 75 were used to prepare a series of substituted dienes in excellent yields through the addition of a-sulphinyl carbanions, Brook rearrangement and expulsion of sulphinate, in a reaction pathway recognisably more typical of acyl silanes (Scheme 117). 

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See also in sourсe #XX -- [ ]

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