Synthesis of Chiral 1,4‐Benzodioxanes and Chromans by Enantioselective Palladium‐Catalyzed Alkene Aryloxyarylation Reactions

Abstract

A highly enantioselective alkene aryloxyarylation led to the high-yielding formation of a series of 1,4-benzodioxanes, 1,4-benzooxazines, and chromans containing quaternary stereocenters with excellent enantioselectivity. The sterically bulky and conformationally well defined chiral monophosphorus ligand L4 or L5 was responsible for the high reactivity and enantioselectivity of these transformations. The application of this method to the synthesis of the chiral chroman backbone of α-tocopherol was demonstrated.

Recent Developments in Pd0‐Catalyzed Alkene‐Carboheterofunctionalization Reactions

“…Ta ng and co-workers recently described ar elated asymmetric alkene-carboalkoxylation reaction of alkenyl phenols 55 to form 1,4-benzodioxanes, 1,4-benzooxazines, and chromans 56 by using ac atalyst that was composed of [Pd 2 (dba) 3 ]a nd Pchiral phosphine ligand 57 (Scheme 18). [27] The highestl evels of asymmetrici nduction were obtained by using hexafluorobenzene as the solvent. Substrates that contained aheteroatom in the homoallyl chain were well-toleratedu nder the reaction conditions.…”

Effects of ligands on the migratory insertion of alkenes into rhodium–oxygen bonds

“…[10][11][12] However, related information on the insertions of alkenes into metal-oxygen bonds is lacking. 13,14 The insertions of alkenes into metal-oxygen bonds has been demonstrated to occur during several important catalytic reactions, [15][16][17][18][19][20][21][22][23][24][25][26] including the classic Wacker oxidation under conditions of low chloride concentration, [27][28][29][30][31][32] but examples of discrete complexes that undergo insertions of olens into metalalkoxide bonds are rare and have occurred in most cases with activated alkenes. For example, tetrauoroethene inserts into the platinum(II)-methoxo bond of Pt(DPPE)(OMe)(Me) (Scheme 1A), 33 acrylonitrile inserts into the platinum(II)-phenoxo bond in Pt(PEt 3 ) 2 (OPh)(H), 34 and tetracyanoethene inserts into the Pt(II)-O bond of a platinaoxetane.…”

Efficient syntheses of (−)-crinine and (−)-aspidospermidine, and the formal synthesis of (−)-minfiensine by enantioselective intramolecular dearomative cyclization

“…We proposed that a chiral monophosphorus ligand developed in our laboratory could provide excellent reactivity, chemoselectivity and enantioselectivity for this challenging reaction. 11 Bromide III could be synthesized from the readily available aryl aldehyde 6 and aniline 7 by a reductive amination process.…”