Stereochemical control in the ester enolate Claisen rearrangement. 1. Stereoselectivity in silyl ketene acetal formation

An improved synthesis of a ring-C precursor to cobyric acid

“…5 These results mirror those we obtained previously with a related system. 1c Gratifyingly, however, excellent selectivity was achieved employing a slight modification of conditions recently reported by McIntosh et al 9 Adapting this methodology, E-enolate formation was carried out with freshly prepared KHMDS and TBSOTf in Et 2 O at -78 °C.…”

23‐Oxa‐Analogues of OSW‐1: Efficient Synthesis and Extremely Potent Antitumor Activity

“…The lithium E enolate of ethyl propionate was generated by the method described by Ireland et al [13] When 7 was treated with this enolate (A, Scheme 3), only the expected 17a-hydroxy-21a-methyl product 8 a was produced (in 63 % yield). Without the use of stereocontrol to generate exclusively the E enolate of ethyl propionate (B, Scheme 3), the condensation reaction predominantly led to the desired 21a-methyl product 8 a (75 % yield), but its 21b-methyl isomer 9 a was also isolated in 12 % yield.…”

Intramolecular Diels‐Alder Reaction of 8‐Trifluoromethyl‐1,3,8‐Nona‐Trienes: An Access to Angular Trifluoromethylated Hydrindenes

“…crotyl propanoate) a highly reliable and predictable transfer of stereochemistry from starting material to product can be realized through an efficient control of ketene acetal geometry. 24 The corresponding Claisen rearrangement of crotyl3-methyl-2-butenoate (a case of ester dienolate anion) was investigated by Wilson in 1975 and shown to be less stereoselective (68% for the trans-crotyl derivative) than the usual Claisen rearrangement (B5°/0)25…”