Intramolecular allylsilylation

In the presence of hafnium tetrachloride/trimethylchlorosilane catalyst, alkynyl allylsilane compounds undergo an intramolecular allylsilylation reaction to give cyclic alkenylsilanes in good yields ... 

Intramolecular allylsilylation of alkynes is a convenient route to cyclic vinylsilanes.211 Propargylsilanes are available for Lewis acid-promoted carbosilylation of alkynes.212 Unlike allylsilanes, both cr-substituted and unsubstituted propargylsilanes react at the a-position, which can be rationalized by in situ isomerization of these reagents to allenylsilanes (Equation (55)). 

Intramolecular allylsilylation of alkynes is a convenient route to cyclic vinylsilanes. The HfCU-MesSiCl catalyst system effectively induces endo cyclization of al-kynylated allylsilanes to l-silyl-3-vinylcycloalkenes (Scheme 10.193) [515]. The endo selectivity is probably because the exo cyclization pathway via zwitterionic intermediate 144 is inhibited by a severe steric repulsion between the substituent R and the allylsilane moiety. 

Scheme 3-48. Hafnium-catalyzed intramolecular allylsilylation of alkynes.

Allylic silanes 20 containing an alkynyl moiety undergo intramolecular allylsilylation in the presence of a HfCl4/Me3SiCl catalyst system to produce five-, six-, and... 

Trans-1 -allyl-2-(trimethylsilyl)cyclopentane and trans-1 -allyl-2-(trimethylsilyl)-cyclohexane are formed from the reaction of la with cyclopentene and cyclohexene, respectively. A second allylsilylation reaction of these compounds with la also gives unusual allylsilylation products, 7-cyclopent-l-enyl-2,2-dimethyl-4-(trimethylsilyl-methyl)-2-silaheptane (30%) and 4-((cyclohex-l-enyl)methyl)-2,2,8,8-tetramethyl-2,8-disilanonane (39%). As observed in the allylsilylation of 4-(trimethylsilyl-methyl)-l-alkenes, these products are likely formed via intramolecular silyl rearrangements. In this case, the results strongly suggest that a 1,5-silyl shift and... 

One of the important advantages of the intramolecular alkene silylformylation reaction as an aldol equivalent is that the products are masked 3,5-dihydroxyalkanals, and therefore that no manipulations are required prior to iteration of the process by aldehyde al-lylation to set up the next intramolecular silylformylation. Given that allylsilanes are well-known aldehyde allylation reagents, intramolecular silylformylation employing a diallylhydrosilane would, in principle, allow for the possibility of a tandem silylformyla-tion/allylsilylation reaction. This has been reduced to practice the diaUylsilyl ethers 60 were subjected to the previously developed silylformylation conditions and the unpuri-fied reaction mixtures were subjected to the Tamao oxidation ]36] to provide triols 61... 

The allylsilyl-substituted diazoester 1, while stable thermally up to 140 C and towards Rh2(pfb)4, undergoes a photochemically induced intramolecular cyclopropanation reaction leading to the rather strained 2-silabicyclo[2.1.0]butane 17 in surprisingly good yield [9]. 

---