A Convergent Route to the Galbulimima Alkaloids (−)‐GB 13 and (+)‐GB 16

Abstract

Alkaloids all round: A 19‐step total synthesis of the galbulimima alkaloid (−)‐GB 13 starting from commercially available starting material and the first total synthesis of the galbulimima alkaloid (+)‐GB 16 have been achieved (see scheme; Boc=tert‐butoxycarbonyl).

Enantioselective Syntheses of Heteroyohimbine Natural Products: A Unified Approach through Cooperative Catalysis

“…Tr ace amounts of product were observed after 120 hw hen using stoichiometric a-methylbenzylamine (E,entry 5), which has been utilized previously in similar systems, [20] but again, we desired much more rapid conversion with high levels of selectivity.T ot his end, we sought to utilize an additive to activate the unreactive enoate electrophile and drive conversion.…”

“…Given all of this innovation, it is surprising that asymmetric intramolecular Michael additions [19] into simple unsaturated esters still remain underexplored, with reported examples typically involving stoichiometric amine and extended reaction times (3-4 weeks). [20] In our studies to form trans-piperidine 15,w ef irst used stoichiometric pyrrolidine (Table 1, entry 1) with linear precursor 16 (obtained in 41 %y ield over four steps from 3-amino-1-propanol;s ee the Supporting Information, SI) to obtain (AE)-15.…”

Enantioselective Syntheses of Heteroyohimbine Natural Products: A Unified Approach through Cooperative Catalysis

“…Tr ace amounts of product were observed after 120 hw hen using stoichiometric a-methylbenzylamine (E,entry 5), which has been utilized previously in similar systems, [20] but again, we desired much more rapid conversion with high levels of selectivity.T ot his end, we sought to utilize an additive to activate the unreactive enoate electrophile and drive conversion. Tr ace amounts of product were observed after 120 hw hen using stoichiometric a-methylbenzylamine (E,entry 5), which has been utilized previously in similar systems, [20] but again, we desired much more rapid conversion with high levels of selectivity.T ot his end, we sought to utilize an additive to activate the unreactive enoate electrophile and drive conversion.…”

“…Known chiral secondary amines (entries 2-4) were evaluated, but these sterically congested amines surprisingly did not afford any desired product in areasonable time (< 120 h). Tr ace amounts of product were observed after 120 hw hen using stoichiometric a-methylbenzylamine (E,entry 5), which has been utilized previously in similar systems, [20] but again, we desired much more rapid conversion with high levels of selectivity.T ot his end, we sought to utilize an additive to activate the unreactive enoate electrophile and drive conversion.…”

“…[14] Form ore challenging transformations,a dditives such as Brønsted acids, [15] H-bond donors, [16] and Lewis acids, [17] which generally facilitate conversion by activation of the electrophile, [18] are employed. [20] In our studies to form trans-piperidine 15,w ef irst used stoichiometric pyrrolidine ( Table 1, entry 1) with linear precursor 16 (obtained in 41 %y ield over four steps from 3-amino-1-propanol;s ee the Supporting Information, SI) to obtain (AE)-15. [20] In our studies to form trans-piperidine 15,w ef irst used stoichiometric pyrrolidine ( Table 1, entry 1) with linear precursor 16 (obtained in 41 %y ield over four steps from 3-amino-1-propanol;s ee the Supporting Information, SI) to obtain (AE)-15.…”