Acyclic stereoselection—13

Enolboration. 6. Dicyclohexyliodoborane, a Versatile Reagent for the Stereoselective Synthesis of Either Z or E Enolates from Representative Esters

“…9 The sterically hindered aryloxy groups have also been used in the enolization of esters with LDA to achieve the synthesis of anti aldols. 12 Even though there are a few reports indicating the effect of sterically hindered carbonyl substituents favoring the E enolate geometry, no systematic study has been reported to understand this important stereodirecting effect. Such an effect is especially valuable in the case of esters, since the synthesis of an ester with a suitable alkoxy group is usually quite easy by trans esterification.…”

Tether-directed synthesis of highly substituted oxasilacycles via an intramolecular allylation employing allylsilanes

“…(Scheme 5). [18] We were concerned, however, that the steric bulk of the aryl ester in 5b , which is required to impart the complete anti selectivity on the aldol reaction, would make unmasking of the aldehyde difficult owing to unfavourable steric clashes between the carbonyl group and one of the tert -butyl groups in the aryl ring forcing the aromatic group to rotate out of the plane of the ester, leaving the bulky tert -butyl groups to flank the faces of the carbonyl and block the Bürgi-Dunitz approach trajectory of the reducing agent. We therefore chose to investigate this reduction step on the model substrate 6b , where the TES-ether would function as a cheaper mimic of the tethered allylsilane in our desired system.…”

Isomerisation of (E)‐2‐Tetrahydrofurylidenealkanecarboxylic Esters and Amides into Their (Z) Isomers by Chelation Control with Metallated Bases or Lewis Acids

“…Starting materials not mentioned below were commercially available. The following compounds were prepared according to published procedures: 2,6-Di-tert-butyl-4-methylphenyl propionate and 2,6-dimethylphenyl propionate, [9] isopropyl propionate. [ …”