Brook rearrangement derivative reactions

It is worth mentioning that in a few cases the (3-elimination of the silyl radical from the a-silyl alkoxyl radical (47) with the formation of corresponding carbonyl derivative was observed [63,64]. Evidently the fate of a-silyl alkoxyl radical depends on the method of radical generation and/or the nature of the substrate. Two examples that delineate the potentialities of this rearrangements are reported in Reactions (5.33) and (5.34). In the former, the 5-exo cyclization of secondary alkyl radical on the carbonyl moiety followed by the radical Brook rearrangement afforded the cyclopentyl silyl ether [65], whereas Reaction (5.34) shows the treatment of an a-silyl alcohol with lead tetracetate to afford the mixed acetyl silyl acetal under mild conditions [63]. 

The latter reaction involves the addition of the pcrfluoro(l-iodohexane) to phenyl trimethylsilyl ketone and a Brook rearrangement with lithium fluoride and fluorotrimethylsilane elimination. In the case of the corresponding magnesium derivative, which is more stable at the reaction temperature, warming up to room temperature before hydrolysis is necessary.214... 

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 dilithio derivative of 1,4-bisphenylsufonylbutane 61 was formed prior to the introduction of homochiral acylsilane 56 into the reaction mixture. The nucleophilic carbonyl addition/Brook rearrangement/elimination sequence delivered bis (fi)-vinyl silyl ether 64 in high yield and with very high selectivity through the putative intermediates 62 and 63. This short and effective synthesis of 55, this time made as the major isomer, was then completed as described above for 54. 

The reaction of 5-silyl-y,5-epoxypentanenitrile derivatives with a base and an alkylating agent gives (Z) - 3 - s i I o x y- y, 3 -u n saturated pentanenitrile derivatives via a tandem process that involves the formation of a cyclopropane derivative by epoxy nitrile cyclization followed by Brook rearrangement and an anion-induced cleavage of the cyclopropane ring (Scheme 105).152... 

One of the most used sequential component reactions in the asymmetric construction of chiral compounds is the so-called anion relay chemistry (ARC) [2], This linchpin coupling protocol consists in the alkylation of an anion, generally a silyl lithium dithiane derivative, by an epoxide or an aziridine, resulting in an oxy- or aza-anion, which in the presence of hexamethylphosphoramide (HMPA) or other polar solvent gives a 1,4-Brook rearrangement, thereby leading to a new reactive dithiane anion that is capable of reacting with a second electrophile E+ (Scheme 11.1). 

Deep-seated rearrangements have likewise been known to occur during lithium aluminum hydride reduction of epoxides. Among thw is the interesting reaction reported by Barton and Brooke i involving the morolic acid derivative shown in Eq. (402). 

Brooke GM Ferguson JAKJ (1986) Partially fluorinated heterocyclic compounds. Part 22. The preparation of allyl 2,5,6-trifluoropyrimidin-4-yl ether and related compounds and a study of their Claisen rearrangement reactions. A new route to 5-fluorouracil and barbituric acid derivatives. J Chem Soc Perkin Trans 1 515-520... 

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