Stereoselective Addition of Organocopper Reagents to Cyclic N-Acyliminium Ions.

Rhodium-Catalyzed Cyclohydrocarbonylation: Application to the Synthesis of (+)-Prosopinine and (−)-Deoxoprosophylline

“…Lithiation of 14 followed by transmetalation to copper and the subsequent addition of BF 3 etherate generated the alkylcopper·BF 3 complex 16 in situ . The addition of 2-ethoxypiperidine 11 to the ether solution of 16 gave the fully protected (+)-prosopinine 17 in 42% for 4 steps (Scheme ).…”

Stereocontrolled Addition of π-type Nucleophiles to a Bicyclic N-Acyliminium Ion. New Access to trans-2,6-Disubstituted Piperidine Substructures

“…4 This result has been attributed to A (1,3) strain. 3 Similar facial selectivities have been observed with homologous N-acyliminium ion stemming from proline derivative 1. 5 In sharp contrast with these observations, we recently showed that nucleophilic additions of π-type nucleophiles to bicyclic aminoether 3 in the presence of a Lewis acid, afforded trans pyrrolidine derivatives generally with high selectivity.…”

“…2,3 The most stereoselective method reported for the synthesis of these latter compounds consists in the nucleophilic addition of alkylcopper reagents to the N-acyliminium ion obtained from the pipecolic acid derivative precursor 2. 3 However, when the latter is treated with synthetically more versatile π-type nucleophiles, the cis stereoisomers are selectively obtained (de >90%). 4 This result has been attributed to A (1,3) strain.…”

“…3 However, when the latter is treated with synthetically more versatile π-type nucleophiles, the cis stereoisomers are selectively obtained (de >90%). 4 This result has been attributed to A (1,3) strain. 3 Similar facial selectivities have been observed with homologous N-acyliminium ion stemming from proline derivative 1.…”

“…7 The required iminium precursor 4 was obtained starting from L-lysine according to a previously reported procedure 8 involving an electrochemical key-step. 3,4 The reactivity of this compound towards various commercially available π-type nucleophiles including allyltrimethylsilane, cyanotrimethylsilane, silyl enol ethers, furan and indole was investigated (Table 1). Mixtures of aminoether 4 and of the nucleophile were treated with appropriate Lewis acids 9 giving rise to compounds 5 via the nucleophilic addition onto N-acyliminium intermediate I (Scheme 1).…”