The Homo-Brook Rearrangement

The spirocompounds 34 (M = Ti or Zr) have been prepared . Studies of the thermolysis of pentacoordinate 1,2-oxasiletanides 35, potential intermediates in both the Peterson reaction and the homo-Brook rearrangement of p-hydroxyalkylsilanes with bases, in the presence of a proton source afforded the olefin, RCH=C(CF3)2 and/or the alcohol, (CF3)2CHOH <99CL1139>. 

Under certain conditions (KH in HMPA), products from the homo-Brook rearrangement are observed (eq 2). This is therefore a good method of desilylation of -hydroxy vinylsilanes to the... 

Treatment of a-methoxy- -hydroxyalkylsilanes 203a and 203b with KOBu in aqueous DMSO yields the methoxy alcohols 204a and 204b, respectively, with high isomeric purity (Scheme 2.129) [20]. The protodesilylation involved in the homo-Brook rearrangement takes place with completely stereospedfic retention of configuration at carbon. 

The homo-Brook rearrangement readily occurs when l-(l-hydroxyalkyl)- -alkenylsilanes 205 are treated with NaH in HMPA (Scheme 2.130). The re-... 

Treatment of the resulting carbanion with various electrophiles instead of protonation affords the corresponding adducts [363-365]. Successive addition of the a-silyldibromomethyllithium 207 and HMPA to esters causes the homo-Brook rearrangement providing carbanions of the alkyl silyl mixed acetals 208 (Scheme 2.132). Quenching with various electrophiles effectively yields the corresponding alkyl silyl acetals 209. 

Naganuma, K., Kawashima, T., Okazaki, R. Control factors of two reaction modes of pentacoordinate 1,2-oxasiletanides, the Peterson reaction and homo-Brook rearrangement. Chem. Lett 1999, 1139-1140. 

Another instance of successful homo-Brook rearrangement occurred in a total synthesis of the antitumor agent FR66979. Here the tendency for Peterson elimination from -hydroxysilane 99 was overcome by the countervailing aziridine-opening pathway, providing the ring-expanded product 100. "... 

A homo-Peterson process intervened upon 1,4-rearrangement of the alkoxide formed by addition of tris(trimethylsilyl)methyllithium 124 to styrene oxide. The resulting carbanion 125 led mainly to the homo-Peterson product 126, with some of the adduct 127 from addition to a second equivalent of the epoxide. In their report, Fleming and co-workers noted that the homo-Peterson reaction is probably favored in this case by the benzylic positioning of the silyloxy group in 125, and they discussed the parallel between the Peterson olefination and a 1,3-Brook rearrangement process. ... 

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