Synthesis of a Butyrolactone Precursor of an Algae Nonaether from an Enantiopure Glycol Obtained by Hoppe's Chemistry

The Preparation of Nonracemic Secondary α-(Carbamoyloxy)alkylzinc and Copper Reagents. A Versatile Approach to Enantioenriched Alcohols

“…A spectacular development in this field was achieved by Hoppe et al, who demonstrated that the complex s BuLi/ (−)-sparteine could induce the enantioselective deprotonation of achiral alkyl carbamates. , The chiral lithium species thus formed can be alkylated with retention of configuration to give the protected secondary alcohols in high ee’s. The use of these lithium species has so far been limited as a result of their configurational lability above −70 °C, although Hoppe and others have reported various applications of this methodology.…”

Asymmetric Deprotonation with Alkyllithium–(−)‐Sparteine

“…However, the double-branched tert-butyl residue in 29 completely suppresses the (−)-sparteine-mediated deprotonation 37 . Non-conjugated double bonds 38,39 (30, 31a), γ -phenyl 4, 40 (32a) or ferrocenyl 41 residues (34a) do not give rise to a selectivity change. The strongly directing power of the carbamoyloxy group is best seen in a deprotonation experiment with the 3-(2-methoxyphenyl)propyl carbamate 33a 4,42 : Although the compound holds further-in a thermodynamic sense-more acidic positions at the aryl ring and in the benzylic position, it is exclusively deprotonated adjacent to the carbamate group.…”

Indolizidine and quinolizidine alkaloids

“…Recent applications of Hoppe's methodology include syntheses of N-Boc-protected phenylglycines, 135 and of enantiopure 5-substituted butyrolactone intermediates en route to an algal nonaether. 136 Cuprates made from sparteine-complexed 2-lithio-N-Boc-pyrrolidine coupled efficiently with vinyl or propargyl iodides, 137 and copper(i) cyanide catalysed the palladium-induced coupling of the same lithiated intermediate with aryl and vinyl iodides; 138 interestingly, the enantioselectivities of these processes were not determined. Other useful transformations involving (2)-sparteine-mediated deprotonation include a highly enantioselective enolborination of prochiral and racemic cyclohexanones to give products such as 260 and 261 (ee ca.…”