Synthesis and absolute configurations of halogenoallenes

Abstract

The highly stereoselective synthesis of 3-methyl-l-halogenoallenes, 3-tert-butyl-l-halogenoallenes, and 1,3di-iert-butylallene is described. The R absolute configuration is assigned to the levorotatory halogenoallenes by relating them to alienes of known configurations. The configurational assignments are in agreement with (vacuum) circular dichroism data for the tert-butylallenes. The obtained results are used to clarify the hitherto existing confusion in the literature concerning absolute configurations of chloroand bromoallenes. Further, the signs and magnitudes of the ligand specific parameters for the halogens in the chirality functions approach, used to predict optical rotations of alienes, are discussed. The literature parameter for chlorine is revised and adequate numerical values for those of bromine and iodine are proposed.Recently, a synthetic route to optically active 3phenyl-1-halogenoallenes 1 and 21-halogeno steroidal alienes 2 of high enantiomeric purity has been described.2,3The present investigation demonstrates the utility of the method to obtain optically active 3-alkyl-1-halogenoallenes, viz., 3-tert-butyl-l-halogenoallenes 3a-c and 3-methyl-lhalogenoallenes 4b and 4c. These compounds, together with 1,3-di-tert-butylallene 3d, are very interesting from a theoretical point of view, particularly in relation to theoretical treatments of optical rotations of alienes.4,5

A Highly cis-Selective Synthesis of 2-Ethynylaziridines by Intramolecular Amination of Chiral Bromoallenes: Improvement of Stereoselectivity Based on the Computational Investigation

“…3 Among them, the organocopper-mediated substitution of bromoallenes is extremely useful in that the substitution of propargylic oxygen by an alkyl group can be carried out with overall retention of configuration: 1c,d both the bromination of propargyl esters with CuBr/LiBr 4 and alkylation of the resulting bromoallenes by organocopper reagents proceed with inversion of configuration. 5 In contrast, the reaction of bromoallenes with nitrogen nucleophiles is relatively limited. Although the intermolecular amination of racemic bromoallenes has been already reported, 6 an intramolecular reaction and a stereochemical course of the amination toward chiral bromoallenes are unprecedented as far as we are aware.…”

An integrated approach using UHPLC–PDA–HRMS and 2D HSQC NMR for the metabolic profiling of the red alga Laurencia: Dereplication and tracing of natural products

“…The relative configuration at C-4 could not be established through analysis of the spectroscopic data. According to Lowe's rule (Elsevier et al, 1985;Lowe, 1965), the negative sign of the optical rotation measured for compound 1 suggested the absolute configuration of the bromoallene moiety to be R.…”

“…In particular, the NOE cross-peaks of H-3/H-5, H-4/H-14, H-5/H-13, H-12/H 3 -15 and H-13/H 3 -15 suggested the relative configurations of the asymmetric centers as 4R ⁄ ,5R ⁄ ,12R ⁄ ,13S ⁄ ,14S ⁄ . The absolute configuration of the bromoallene moiety, according to Lowe's rule (Elsevier et al, 1985;Lowe, 1965), was determined as R on the basis of the negative sign of the optical rotation measured for metabolite 2.…”

Development of Useful Reactions Involving Tandem Cyclizations Based on the Novel Reactivities of Allenic Compounds

“…135) Among them, the organocopper-mediated substitution of bromoallenes is extremely useful in that the substitution of propargylic oxygen by an alkyl group can be carried out with overall retention of configuration 136) : both the bromination of propargyl esters with CuBr/LiBr 137,138) and alkylation of the resulting bromoallenes by organocopper reagents proceed with inversion of configuration. 139) In contrast, the reaction of bromoallenes with nitrogen nucleophiles is relatively limited. Although the intermolecular amination of racemic bromoallenes has been already reported, [140][141][142] an intramolecular reaction and a stereochemical course of the amination toward chiral bromoallenes were unprecedented.…”