Kinetics, stereochemistry, and mechanisms of the silaalylic and silapropynylic rearrangements

Diastereoselective Synthesis of Seven-Membered-Ring trans-Alkenes from Dienes and Aldehydes by Silylene Transfer

“…On the other hand, heating the trans -alkenes at 60 °C reduced the half-life to 30 minutes and improved its yield (Table 1). The ease of this transformation compared to known 1,3-silyl rearrangements 26 provides additional confirmation that the cyclic trans -alkene is highly strained. …”

“…This [1,3]-silyl rearrangement to a stable oxasilacyclopentene, which would be expected to require high temperatures (500 °C), 26 occurred readily at room temperature in most cases. In the case of the trans -alkene derived from 3-methylpentadiene, isomerization did not occur, which is likely because this product would be sterically congested (eq 3).…”

Metalation of 9‐Oxabicyclo[3.3.1]nonadiene – the Deprotonation Path to Bridgehead Olefins

“…In the case of carbon, diradical intermediates are involved. [27] In contrast, sigmatropic shifts of allylsilanes have been shown to be suprafacial rearrangements that occur with inversion of the silicon configuration according to experimental results, [28] while theory would favor retention of the configuration. [29] The same should be true for allylgermanes and allylstannanes.…”

“…Stripping the solvent at reduced pressure in the last step gave a colorless oil (0.12 g) containing compounds 5 and 6a in the ratio 3:7. . 29 Si NMR (79 MHz, C 6 D 6 ): δ = 4.8 ppm (see Table S2 13 C NMR (100 MHz, C 6 D 6 ): δ = 155.4 (C-1), 131.4 (C-7), 130.7 (C-6), 123.2 (C-2), 81.9 (C-5), 33.6 (C-4), 30.8 (C-8), 28.4 (C-3), -3.8 ppm (CH 3 ). 29 Si NMR (79 MHz, C 6 D 6 ): δ = 7.8 ppm (see Table S2 Formation of 1-Trimethylplumbyl-9-oxabicyclo[3.3.1]nona-2,6-diene (7) and 3-exo-Trimethylplumbyl-9-oxabicyclo[3.3.1]nona-1,6-diene (8a): All synthetic steps were carried out as described for the stannyl derivatives under Procedure A, except that solid Me 3 PbCl (3.5 g, 12.2 mmol) was used for quenching the anion derived from 1.…”

Theoretical studies on the gas-phase pyrolysis of 2-trimethylsilylethanol

“…Scheme 1 shows two possible geometries of the pentacoordinated silicon -trigonal bipyramidal (TBP) and square pyramidal (SP) structures. Accordingly, for the concerted 1,3-silyl migration in allylsilane [4,5], there may be two possible suprafacial pathways with different stereochemical configurations at silicon, where the transition state(TS) with inversion of configuration (TS inv ) has a TBP structure and the TS with retention of configuration (TS ret ) has a SP structure. It was recognized that the thermal 1,3-silyl migration in both allylsilane and formylmethylsilane should proceed concertedly via the four-membered cyclic TSs with retention of configuration at silicon (TS ret ) [4], and the calculated activation energies were in good agreement with experimental results.…”