Silatropic rearrangement

The mechanistic study of this reaction has also shown that in the case of a substituted allyl group an exocyclic [l,3]-silatropic rearrangement is in competition (.Ea = 173-176 kJmol-1) with the endocyclic retroene reaction6. Thus the yield of silole reaches at most about 40%. However, this method can be used for the synthesis of C-methylated siloles having a Si—H bond (see Section II.B.2.e). 

Facile migration of silyl groups in 5-silylcyclopentadienes is usually referred to as fractional 1,2-silyl rearrangement or 1,5-suprafacial silatropic rearrangement (equation 39). The fundamentals of this migration have been well discussed in BB1. Several examples of this type of migration have also appeared in recent papers95-105. 

Our first approach [51] to azetidine-2,3-diones relies on the silatropic rearrangement of trimethylsilyl a-hydroxyacetates 87 into the thermodynamically more stable a-trimethylsilyloxyacetic acids 88. The [2 H- 2] cycloaddition step was carried out by means of phenyl dichlorophosphate reagent in yields being in the range 40-65%. Under these conditions, the P-lactam 91 was produced in 45% yield as the single cis isomer. To transform 91 into 93 dimethylbromosulphonium bromide-triethylamine system [52] furnished the desired a-keto P-lactam in 90% yield. 

Without additional reagents Regiospecific silatropic rearrangement Enoxysilanes... 

An interesting condensation reaction to afford a polymer with P=C bonds has been recently reported [28]. The reaction involves a [1,3]-silatropic rearrangement (Fig. 5.20). 

The reaction between 1-diazopropanone and (113) leads to a cyclopropane, but rapid silatropic rearrangement prevents its isolation, and the Py-enol ether (114) is... 

EXSY NMR spectroscopy to undergo 1,5-shifts. Silatropic rearrangements of tetrahydro-4,4,8,8-Me4-4,8-disila-5ym-indacene have been established using... 

Additionally, the authors propose a potential silatropic rearrangement to be involved. These mechanistic considerations were supported by crossover experiments that are consistent with silicon released from the nucleophile and formation of a new, chiral Lewis acid in combination with the employed Brpnsted acid. Therefore, the active Lewis acid is generated in situ and is regenerated during the catalytic cycle. 

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