Mechanisms of thermolytic fragmentation of allyl ethers. I

The Stereoselective Synthesis and the Nitrogen Interconversion Studies of 2-(tert-butoxymethyl)-1-[NT-(4-methylbenzenesulfonyl) (4-methylphenoxy) imidoyl] aziridine

One-pot synthesis of the title compound (1) is achieved from tert-butyl allyl ether (2) and the N'(4-methylbenzenesulfonyl) (4-methylphenoxy) imidoyl azide (3) in high yield. The energy barrier of nitrogen interconversion of the title compound (1) was investigated by dynamic NMR. The free energies of activation (A G‡) are 11.11 kcal/mol ( Tc = 238 K) and 11.30 kcal/mol ( Tc = 242 K) in acetone-d6 and chloroform-d, respectively, and are attributed to nitrogen inversion of aziridine ring nitrogen.

Synthesis of unsymmetrical alkyl acetals via addition of primary alcohols to allyl ethers mediated by ruthenium complexes

ABSTRACT

Ru-catalyzed synthesis of mixed alkyl-alkyl acetals via addition of primary alcohols to allyl ethers has been extended to include long-chain and/or functionalized substrates. The catalytic systems for these reactions were generated from RuCl₂(PPh₃)₃ and [RuCl₂(1,5-COD)]_x and phosphines [PPh₃ or P(p-chlorophenyl)₃] or SbPh₃. Of particular importance is the almost quantitative elimination of transacetalization. The addition proceeds through allyl complexes, not via isomerization of allyl ethers--subsequent addition of ROH to vinyl ethers.

GRAPHICAL ABSTRACT

Substituent Effects on Vinyl Radical Cyclizations onto Aryl Rings

Regioselective toluenesulfanyl radical addition to the C-1 carbon of propynyl benzyl ethers 2a-i leads to vinyl radicals 3a-j which mainly give methyl sulfides 9a-j and methyl ethers 8a-j through stereoselective 5-(pi-endo)exo and 5-(pi-exo)exo cyclization, respectively. Additionally, minor amounts of pi-endo 6-membered cyclization products 5a-j and hydrogen abstraction products 4a-j are also formed. The role of steric and stereoelectronic factors in the 5-membered vs 6-membered and pi-endo vs pi-exo cyclization as well as the role of stabilization and polar factors has been studied. The substituent effect on the 5-(pi-exo)exo cyclization has been estimated by the relative rate constants, k(R), calculated for several substituents in the 4- and 3-position. Results show that stabilization and polar factors slightly affect the rate of the vinyl radical cyclization onto arene rings, which appears to be rather unselective with respect to the nature of the substituent. The nature of polar effects indicates that vinyl radicals are slightly electrophilic in character.