Stereo- and Regiochemistry of Aldehyde Insertions into the C-Si Bonds of Siliranes

Abstract

During investigations of the basic reactivity of siliranes, Seyferth observed that hexamethylsilirane (1) undergoes insertion of aldehydes to afford oxasilacyclopentane 2 (eq l).1•2 345678Since this silirane was the only one examined, the stereochemistry and regiochemistry of this carbon-carbon bond-forming process have not been investigated, although this information would provide vital clues about the reaction mechanism. In fact, little is known about the scope of silirane chemistry.2-8 We have discovered that siliranes undergo stereochemically and regiochemically defined insertions of aldehydes, and the outcome is determined by the reaction conditions. Furthermore, siliranes were used for the synthesis of diols such as 4 in two steps (aldehyde insertion and oxidation) from the silirane trans-3, which can be obtained by silacyclopropanation of (£>2-butene (eq 2).9

Anion Relay Chemistry: Access to the Type II ARC Reaction Manifold through a Fundamentally Different Reaction Pathway Exploiting 1‐Oxa‐2‐silacyclopentanes and Related Congeners

“…Ito [9] and Woerpel [10] exploited the Tamao–Fleming oxidation to furnish 1,3-diols; Hiyama, [11a] Tamao, [11b] and Denmark [11c,d] achieved Hiyama-type palladium-catalyzed cross-coupling reactions induced by fluoride; and both Roush [12] and Schreiber [13] employed 1-oxa-2-silacyclopentanes as templates for intramolecular Diels–Alder reactions. More recently, Trost [14] and Lee [15] exploited 1-oxa-2-silacyclopentanes respectively both to access aldoltype products and to achieve anionic desilylation followed by C-alkylation, the latter induced by fluoride ion.…”

“…Pleasingly, the cross-coupling reactions proceed at room temperature. Although the literature provides many examples of 1-oxa-2-silacyclopentanes reacting to yield products of protodesilylation, [19] oxidative desilylation [9, 10] and cross-coupling, [11] few reports of C-alkylation have been described. [15] …”

2‐Arylsilacyclobutane as a Latent Carbanion Reacting with CO2

“…For example, silacyclopropane has a strain energy of 150 kJ mol −1 , which is larger than that of cyclopropane (117 kJ mol −1 ) . Whereas ordinary tetraorganosilicon compounds generally fail to add across the carbonyl group of aldehydes, silacyclopropanes act through ring opening when either heated at 100 °C, or photolyzed, or treated with t BuOK/18‐crown‐6, or treated with a copper salt . A carbonyl insertion reaction can also take place with silacyclopropanes and formamides upon heating .…”

2‐Arylsilacyclobutane as a Latent Carbanion Reacting with CO2

“…[3] Thes train energy inherent in three-and four-membered ring structures often brings forth unique reactivities that are not available with the corresponding acyclic structures.T his also applies to organosilicon compounds. [4,5] Fore xample, silacyclopropane has astrain energy of 150 kJ mol À1 ,which is larger than that of cyclopropane (117 kJ mol À1 ). [6] Whereas ordinary tetraorganosilicon compounds generally fail to add across the carbonyl group of aldehydes,silacyclopropanes act through ring opening when either heated at 100 8 8C, [4b] or photolyzed, [4a] or treated with tBuOK/18-crown-6, [4b] or treated with ac opper salt.…”