Reactivity of chiral exocyclic N-acyliminium ions with aromatic derivatives

Synthesis of Tyrosine‐Derived Tetrahydroisoquinolines by Lewis Acid Catalyzed Cyclization of N‐(Phenylsulfonyl)alkyloxazolidinones

“…Following the protocol of Petrini, [13] compounds 9 and 10 were treated with benzenesulfinic acid and various aldehydes to give corresponding α-amidoalkylphenyl sulfones 11 and 12 as diastereomeric mixtures. The results are summarized in Table 1.…”

“…N-[1-(Phenylsulfonyl)alkyl]oxazolidinones 11 and 12 were then cyclized in the presence of TiCl 4 in CH 2 Cl 2 at -78°C [13] to afford target compounds 13 and 14 (Scheme 2). As can be seen from Table 1, the ring closure of starting sulfones 11a-c and 12a-c proceeded uneventfully (Table 1, Entries 1-3, [9][10][11].…”

“…(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) attracted by the conversion of benzyl-substituted oxazolidinones with aldehydes and benzenesulfinic acid to the corresponding N- [1-(phenylsulfonyl)alkyl]oxazolidinones and their Lewis acid mediated ring closure to tricyclic tetrahydroisoquinoline derivatives published by Petrini. [13] This approach was used for the synthesis of azapodophyllotoxin [14] starting from DOPA. [13b] To the best of our knowledge, however, in no case was either p-or m-tyrosine considered as a starting material.…”

1-(N-Acylamino)alkyltriarylphosphonium Salts with Weakened Cα-P+ Bond Strength—Synthetic Applications

“…The presence of a positively charged nucleofugal phosphonium moiety in the close surroundings of the N -acyl group determines its unique chemical properties such as high reactivity in α-amidoalkylations [1,2,3,4,5,6,7,8,9,10]. This type of reactions has enjoyed unflagging interest for years as a synthetic method with great potential, especially valuable for C-C and C-heteroatom bond formation [1,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37]. …”

“…Of course, the reactivity of N -acyliminium cation 2 or N -acylimine 3 toward a nucleophile is also significant [1,2,3]. To produce the proper α-amidoalkylating agents, for instance N -acyliminium cation 2 or N -acylimine 3 from the most popular precursors such as α-amido sulfones (Z = SO 2 Ar), N -(1-benzotriazolil)alkylamides (Z = Bt), and N -(1-alkoxyalkyl)amides (Z = OR), it is necessary to use catalysts, mainly Lewis acids (route a , Scheme 1 (I)) [18,19,20,21,22,23,24,25,29,30,31,32,33,34,35,36,37]. In contrast, 1-( N -acylamino)alkyltriphenylphosphonium salts 1 (Z = Ph 3 P + X − ) do not require the use of acidic catalysts because of the permanent positive charge on the phosphonium group.…”