The first documented study of the borono-Mannich (Petasis) reactions of pinacol allenylboronate is described. The reactions of salicylaldehyde and primary and secondary amines are highly regioselective and give homopropargylamine and α-allenylamine products, respectively. In contrast, glycoaldehyde and chiral α-hydroxyaldehydes give exclusively anti-β-amino-β-allenyl alcohol products, irrespective of the nature of the amine component. These reactions are highly regio-and diastereoselective and can be employed using an enantiomerically enriched α-hydroxyaldehyde without detectable racemization.
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ABSTRACT:The first documented study of the borono-Mannich (Petasis) reactions of pinacol allenylboronate is described. The reactions of salicylaldehyde and primary and secondary amines are highly regioselective and give homopropargylamine and -allenylamine products, respectively. In contrast, glycoaldehyde and chiral -hydroxyaldehydes give exclusively anti--amino--allenyl alcohol products, irrespective of the nature of the amine component. These reactions are highly regio-and diastereoselective and can be employed using an enantiomerically enriched -hydroxyaldehyde without detectable racemization.The boronic acid or borono-Mannich reaction (Petasis reaction)1 is an important, three component reaction, generally performed between an carbonyl component (usually an aldehyde), a primary (1 o ) or secondary (2 o ) amine and an organoboronic acid or related derivative (boronate or potassium trifluoroborate).2 These reactions work most efficiently when the carbonyl substrate is an -hydroxyaldehyde, 2-4 a glyoxylic acid
A highly diastereoselective synthesis (dr = 99 : 1 97 : 3) of enantioenriched anti-α-allyl-β-fluoroamines (ee = 86–92%) has been developed involving a highly diastereoselective Petasis allyl borono-Mannich reaction of (S)- or (R)-α-fluoroaldehydes.
The chemical study of leaf extracts
from Uvaria cherrevensis resulted in the identification
of 11 new polyoxygenated cyclohexenes,
cherrevenols A–K (1–11), and
a new seco-cyclohexene derivative, cherrevenol L (12).
Nine known compounds (13–21) were
also isolated. Three of the isolated compounds are chlorinated polyoxygenated
cyclohexenes. The structures of these compounds were determined using
spectroscopic methods and, in some cases (compounds 2, 6, 8, and 10), single-crystal
X-ray crystallographic structural analysis or chemical correlation
(compounds 6 and 7). Compounds 6 and 7 were both isolated as scalemic mixtures (ee 23–24%).
Three new 2-phenylnaphthalene derivatives, cherrevenaphthalenes A-C (1-3), and a new polyoxygenated cyclohexene derivative, (-)-uvaribonol F (4) together with six known compounds, 5-10, were isolated from the stem and root extracts of Uvaria cherrevensis (Annonaceae). The structures of all isolated compounds were elucidated by spectroscopic analysis. The structures of 3 and 4 were further confirmed by single crystal X-ray diffraction methods. Compound 2 exhibited modest antiplasmodial activity against the P. falciparum stains TM4/8.2 and K1CB1 with IC values of 18.8±3.63 and 23.4±4.08μM, respectively, and weak cytotoxicity to a Vero cell line. Furthermore, compound 4 displayed cytotoxic activity against a KB cell line with an IC value of 22.1±0.42μM but was non-cytotoxic to the Vero cell line. Compound 5 revealed stronger cytotoxicity towards the KB cell line, with an IC value of 5.05±0.86μM and was nearly equally cytotoxic to the Vero cell line.
The three component borono‐Mannich reactions of ethyl glyoxylate, primary or secondary amines and pinacol allenylboronate or potassium allenyltrifluoroborate are highly regioselective and give α‐propargylglycinates. The (S)‐N‐tert‐butylsulfinyl imine of ethyl glyoxylate underwent an indium chloride catalyzed addition reaction with allenyl potassium trifluoroborate in a highly regioselective and diastereoselective manner to give ethyl (S)‐α‐propargylglycinate after N‐deprotection in 97 % ee.
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