A Theoretical Study of Mechanisms of 1,3-Silyl Migration in Formylmethylsilane and Related Migrations. Comparison with Allylsilane

Abstract

Two concerted pathways leading to retention and inversion of stereochemistry at the migrating silicon center were found for the isomerization of formylmethylsilane to siloxyethene by ab initio molecular orbital calculations. The activation energy for the retention pathway has been calculated at the MP2/6-311++G(3df, 2p)//MP2/6-311++G** level to be 32 kcal/mol, which is ca. 30 kcal/mol smaller than that for the inversion pathway. The predicted exclusive retention stereochemistry and the calculated activation energy are in good agreement with the experimental results for a silylmethyl ketone with an optical active silyl group. Remarkable differences in the retention transition structures between the 1,3-silyl migrations in formylmethylsilane and the 1,3-silyl migrations in allylsilane are revealed by detailed analysis of geometries, natural bond orbitals, and the Laplacian (∇2ρ) of the wave function. The retention 1,3-silyl migration in formylmethylsilane is best described as an intramolecular nucleophilic substitution at silicon, while the corresponding 1,3-silyl migration in allylsilane is as an electrocyclic sigmatropic rearrangement controlled by subjacent orbital interactions. For related 1,3-migrations in HC(O)CH2MH3 (M = C, Si, Ge, Sn), the E a values for the retention pathway are much lower than the inversion pathway and they decrease in the following order: M = C ≫ Si > Ge > Sn (as expected from the relative stability of the pentacoordinate structure among the metals). A facile 1,3-migration from carbon to nitrogen in iminomethylsilane is predicted to occur with retention stereochemistry via an intramolecular nucleophilic substitution, which is similar to that in formylmethylsilane.

Alkyne Hydroacylation: Switching Regioselectivity by Tandem Ruthenium Catalysis

“…For example, we investigated the coupling of aldehyde 1b with 1-(trimethylsilyl)propyne 7 for the formation of silyl dienol ether 8 (Scheme 2). A 1,3-silyl migration 27 of intermediate 9 generates a nucleophile that can be used in asymmetric vinylogous aldol reactions. 28 …”

A theoretical study of thermal [1,3]‐sigmatropic rearrangements of 3‐trimethylsilyl‐1‐pyrazoline: Concerted vs. stepwise mechanisms

“…Previous theoretical studies9, 10 showed that the rearrangements of 1a / 1a ′ only undergo via concerted pathways. Our potential energy surface searches using MP2/6‐31G(d) and B3LYP/6‐31G(d) also yielded only two suprafacial concerted transition states ( SR 2a and SI 2a ) in the rearrangement of 2a / 2a ′ (see Fig.…”

“…Takahasi and Kira10 studied the 1,3‐silyl migrations of heterogeneous allylic silanes in which the terminal atom of allylic moiety is substituted either with oxygen or with nitrogen. In the current study, the thermal rearrangement of methylenesilylmethylamine( 1d / 1d ′) in which the center position of allylic moiety is substituted by nitrogen was first considered to understand the effect of the hetero substitution at this particular position.…”

“…However, theoretical studies9 showed that for the thermal 1,3‐silyl migration in the allylic silane, the two concerted mechanisms are both allowed with the retention pathway being lower in energy by ∼9 kcal/mol. Takahashi and Kira10 further showed theoretically that there are also both concerted retention and inversion pathways for the rearrangement of formylmethylsilane ( 1b ) (see Scheme ) with the retention pathway activation barrier of 32 kcal/mol, which is ∼30 kcal/mol smaller than the inversion one. In the case of iminomethylsilane ( 1c ), only the retention pathway was found with the barrier of 39 kcal/mol.…”

Durch sichtbares Licht vermittelte Cycloadditionen von α‐Ketoacylsilanen mit Iminen: Einfache Synthese von β‐Lactamen

“…Für die Erzeugung von Ketenen durch die photochemischen Bedingungen wurden zwei Mçglichkeiten der Umlagerung betrachtet. Ein Prozess beinhaltet eine einstufige [1,3]-Silylverschiebung [20] zur distalen Carbonylgruppe. Alternativ kçnnte ein zweistufiger Mechanismus,d.…”