The SN2 Reaction in the Solid State. An Unusual, BAl2 Aminolysis of an Ester Group in Crystalline (±)-2-Amino-2‘-hydroxy-3‘-(methoxycarbonyl)- 1,1‘-binaphthyl Elucidated by X-ray Diffraction and Isotopic Labeling. New Experimental Evidence for Linearity in SN2 Substitution

Reaction Outcome Critically Dependent on the Method of Workup: An Example from the Synthesis of 1-Isoquinolones

A striking dependence on the method of workup has been found for annulation of benzonitriles ArC≡N to N-methyl 2-toluamide (1), facilitated by n-BuLi (2 equiv): quenching the reaction by a slow addition of water produced the expected 1-isoquinolones 2; by contrast, slow pouring of the reaction mixture into water afforded the cyclic aminals 5 (retaining the NMe group of the original toluamide). The mechanism of the two processes is discussed in terms of the actual H⁺ concentration in the workup. Both 2 and 5 were then converted into the corresponding 1-chloroisoquinolines 3, coupling of which, mediated by (Ph₃P)₂NiCl₂/Zn, afforded bis-isoquinolines 4.

Preparation and structural characterization of trimethyltin(iv) tropolonate. Investigation of a rare methyl-migrational dismutation in the solution, solid and liquid states

The synthesis and structural characterisation, by low temperature X-ray diffraction and solid-state NMR, of the highly reactive monomeric Me(3)Sn(trop) (1) complex has been studied; 1 rearranges into Me(2)Sn(trop)(2) (2) and Me(4)Sn by methyl-transfer dismutation. Based on the NMR kinetic data it appears that complex demethylates faster in the solid and liquid than in dilute CDCl(3) solution, but with a slower rate than in dilute CD(3)OD solution.

Homochiral Oligopeptides Generated by Induced “Mirror Symmetry Breaking” Lattice-Controlled Polymerizations in Racemic Crystals of PhenylalanineN-Carboxyanhydride

The formation of diastereoisomeric libraries of oligopeptides through the heterogeneous polymerization of racemic crystals of phenylalanine N-carboxyanhydride (PheNCA) is reported. The diastereoisomeric compositions of the oligopeptides formed on polymerization of (R,S) crystals incorporating the deuterium-tagged S enantiomer were determined by MALDI-TOF mass spectrometry. The racemic mixtures of the oligopeptides longer than pentamers are represented primarily by diastereoisomers of homochiral sequence and with peptides containing only one heterochiral repeating unit. A mechanism comprising the following three sequential steps to account for this unusual observation is proposed: 1) formation of dimers and trimers at a partially damaged liquid/solid interface, 2) chain propagation that takes place within the bulk of the crystal through a lattice-controlled "zipper-like" mechanism between homochiral molecules arranged in a head-to-tail motif to yield crystalline antiparallel beta-sheets of alternating oligopeptide chains of homochiral sequence of opposite handedness, and 3) enantiomeric cross-inhibition that results in chain termination. Induced desymmetrization of the racemic mixtures of the formed peptides was achieved by the polymerization of the mixed quasi-racemic crystals of (R)-PheNCA, ((S)-PheNCA), and (S)-ThieNCA (3-(2-thienyl)-alanine N-carboxyanhydride) of various compositions. These experiments resulted in the formation of nonracemic libraries of oligopeptides composed of homochiral chains of (R)-Phe and copolymers of randomly distributed (S)-Phe and (S)-Thie sequences. From these findings, we propose a stochastic model for the generation of libraries of nonracemic mixtures of oligopeptides from the polymerization of host (R,S)-PheNCA with racemic mixtures of other guest NCA amino acids dissolved in limited quantities in the crystal.

Topochemical Transketalization Reaction Driven by Hydrogen Bonding

An unusual thermal isomerization of 1,2;3,4-di-O-isopropylidene-myo-inositol to 1,2;5,6-di-O-isopropylidene-myo-inositol was observed in the solid state. A detailed study revealed that this ketal migration is a topochemically driven one. X-ray structure revealed that strong intermolecular hydrogen bonding in the crystal preorganizes the hydroxyl and ketal carbon in a transition-state-like arrangement favorable for the reaction. The 5-OH of each molecule faces the trans ketal carbon of a neighboring molecule at a close distance and an angle of approach near to linearity, making a trigonal-bipyramidal-like arrangement in the crystal, which could facilitate the reaction. This is the first report of a topochemical transketalization reaction.