Steric Effects of the t-Butyl Group in Organosilicon Compounds¹

Structure of 1,3-di-tert-butyl-2,2,4,4-tetraisopropylcyclodisilazane, C20H46N2Si2

“…The insensitivity of the ring geometry to substituent effects raises the question of whether the compound (BUESi.NBu)2 is sterically too crowded to be stable, or whether the steric bulk of the substituents has simply prevented a synthesis by the direct methods so far attempted. In this context, we note that the cyclotrisiloxane (Bu2SiO)3 cannot be prepared by elimination of water from Bu2Si(OH)2 (a reaction which normally occurs very readily for such compounds) and necessitates a multi-step synthetic route (Sommer & Tyler, 1954;Klingebiel, 1981). We have performed simple • calculations in which the Pr groups of (Pr2Si.NBu) 2 are replaced by Bu groups with C-C = 1.53/~ and ideal tetrahedral angles at the central C atom, while retaining the (C2Si.NBu)2 part of the molecule unchanged.…”

Total Syntheses of (2S)-Antafumicins A and B

“…The preparation of the target compounds (1), a mixture of C-4 epimers, was undertaken via lactonization of 2, which was obtained by the addition of phenyl lithium derivative 3 to optically active aldehyde 4. Aryl lithium (3) was derived from 2,4-dihydroxyacetophenone, whereas 4 was obtained from (S)-malic acid via butanolide (6).…”

“…One of the key intermediates (3) was obtained from bromide 10 by regioselective lithiation at the C-3 position of the 2,4-dihydroxyacetophenone moiety based upon convenient halogen-metal exchange. The preparation of 10 from 2,4-dihydroxyacetophenone (5) is shown in Scheme 2.…”

“…Bromide 10 was regioselectively converted to aryl lithium (3) by n-butyllithium, and the nucleophilic addition of 3 to 4 proceeded at the aldehyde carbonyl group at -20°C to give 2 as an equimolecular mixture in a moderate yield.…”

Structure of 2-(1,2-dihydro-1-methyl-2-pyridylidene)-3-(4-ethoxyphenyl)-3-oxopropanenitrile, C17H16N2O2

“…In this context, we note that the cyclotrisiloxane (Bu2SiO)3 cannot be prepared by elimination of water from Bu2Si(OH)2 (a reaction which normally occurs very readily for such compounds) and necessitates a multi-step synthetic route (Sommer & Tyler, 1954;Klingebiel, 1981). We have performed simple • calculations in which the Pr groups of (Pr2Si.NBu) 2 are replaced by Bu groups with C-C = 1.53/~ and ideal tetrahedral angles at the central C atom, while retaining the (C2Si.NBu)2 part of the molecule unchanged.…”