54962-87-7Relevant academic research and scientific papers
Pentadienyl type lithium and potassium species: The regioselectivity of their reactions with electrophiles
Schlosser,Zellner,Leroux
, p. 1830 - 1836 (2007/10/03)
Seven structurally distinct pentadienyl type lithium and potassium compounds were screened against a variety of electrophiles in order to assess the regioselectivity of the trapping reactions. Organoborates and analogs thereof (fluorodimethoxyborane) proved to be perfectly regioreliable attacking only unsubstituted terminal positions and thus providing, after oxidation, exclusively primary allylic alcohols. 2,4-Pentadienyllithiums or -potassiums, that carry a methyl group at the 1- or 3-position, exhibit the same extreme regioselectivity towards halotrialkylsilanes or carbon dioxide. Although the unsubstituted parent compounds combine with such electrophiles still preferentially at the terminal position, considerable proportions of branched products are concomitantly formed as well (1/3-attack ratios ranging from 2:1 to >20:1). Hydroxyalkylating and alkylating reagents such as formaldehyde, oxirane or butyl iodide invariably afford regioisomeric mixtures generally varying in composition between 3:1 and 1:3. The condensation reaction with halotrialkylsilanes appears to follow a concerted (SN2-like) rather than an addition/elimination (ate complex-mediated) mechanism.
A Highly Effective One-Pot Bicycloannulation Methodology for the Synthesis of Berban and Yohimban Systems Based on Organotin-Mediated Three-Component Coupling (N-Acylative Pentadienylation of C=N Bonds)
Yamaguchi, Ryohei,Hamasaki, Takashi,Sasaki, Tohru,Ohta, Tetsuo,Utimoto, Kiitiro,et al.
, p. 1136 - 1143 (2007/10/02)
A highly effective bicycloannulation methodology for the synthesis of berban and yohimban alkaloid systems is described.Three-component coupling reactions of 2,4-pentadienyltin reagents with C=N bonds and α,β-unsaturated acyl chlorides furnish bicycloannulated products in a one-pot operation.For example, the reactions of 2,4-pentadienyltributyltin(1) with isoquinoline derivatives activated by acryloyl chloride afford the tetracyclic (+/-)-allo-berban systems stereoselectively.Similarly, the reaction of 1 with 3,4-dihydro-β-carboline (11) gives the pentacyclic (+/-)-allo-yohimban system.The reaction is not affected by the stereochemistry of the 2,4-pentadienyltin reagent.A new substituted 2,4-pentadienyltin reagent, 3-(hydroxymethyl)-2,4-pentadienyltrimethyltin (19), is prepared via 3-(hydroxymethyl)pentadienyl dianion.The three-component coupling reaction of 19 with 11 and acryloyl chloride affords the (+/-)-allo-16-(hydroxymethyl)yohimban system, from which (+/-)nitraraine is readily synthesized.In addition, 1,3-asymmetric induction leads to the high diastereoselectivity realized in bicycloannulation (up to 94percent de) when (S)-3--3,4-dihydroisoquinoline (27), which is readily derived from L-phenylalanine, is used in the three-component coupling reaction.
N-ACYLIMINIUM CYCLIZATIONS VIA REVERSIBLE 2-AZA-COPE REARRANGEMENTS
Ent, Hugo,Koning, Henk de,Speckamp, W. Nico
, p. 5105 - 5108 (2007/10/02)
The existence of a reversible 2-aza-Cope rearrangement in cyclizations of N-acyliminium ions derived from 1'- and 2'-vinyl-N-(3'-butenyl)-5-hydroxy-2-pyrrolidinones is established.
