Inversion in-situ

LIPASE CATALYZED OPTICAL RESOLUTION COUPLED WITH IN SITU INVERSION SYNTHESIS OF PRALLETHRIN (PYRETHROID) etc. 

Another example employed Mitsunobu reaction for the inversion reaction (Figure 10(b)).A single enantiomer of a (stereo)chemically labile allylic-homoallylic alcohol was obtained in 96% yield and 91% ee from the racemate through a lipase-catalyzed kinetic resolution coupled with in situ inversion under carefully controlled (Mitsunobu) conditions. Using this reaction, the algal fragrance component, (S)-dictyoprolene, was synthesized. 

L = leaving group (e.g. tosylate, triflate, nitrate, MItsunobu-Intermedlate) Scheme 2.9 Kinetic resolution with in-situ inversion... 

In recent decades, there have been many attempts to fabricate CNT/PANI composites [329-337]. The incorporation of nanotubes into PANI can result in novel composite materials with enhanced electrical, electrochemical, and mechanical properties. Eor example, Yu et al. prepared MWCNT/PANI nanocomposites through in situ inverse microemulsion synthesis [334]. Such nanocomposites are characterized by very strong interaction between MWCNTs and conducting polymers. Moreover, MWCNT/PANI core-shell nanowires exhibited better thermal stability and electrical conductivity than the pure PANI. The electrical conductivity of MWCNT/PANI composite containing 1 wt% of MWCNTs increased by one order of magnitude (pure PANI 0.02Scm MWCNT/PANI composite 0.20Scm-i) [334]. 

Lipase-catalyzed optical resolution coupled with in situ inversion synthesis of prallethrin (pyrethroid), etc. 

The allylstannane 474 is prepared by the reaction of allylic acetates or phosphates with tributyltin chloride and Sml2[286,308] or electroreduction[309]. Bu-iSnAlEt2 prepared in situ is used for the preparation of the allylstannane 475. These reactions correspond to inversion of an allyl cation to an allyl anion[3l0. 311], The reaction has been applied to the reductive cyclization of the alkenyl bromide in 476 with the allylic acetate to yield 477[312]. Intramolecular coupling of the allylic acetate in 478 with aryl bromide proceeds using BuiSnAlEti (479) by in situ formation of the allylstannane 480 and its reaction with the aryl bromide via transmetallation. (Another mechanistic possibility is the formation of an arylstannane and its coupling with allylic... 

Recently, an in-depth review on molecular imprinted membranes has been published by Piletsky et al. [4]. Four preparation strategies for MIP membranes can be distinguished (i) in-situ polymerization by bulk crosslinking (ii) preparation by dry phase inversion with a casting/solvent evaporation process [45-51] (iii) preparation by wet phase inversion with a casting/immersion precipitation [52-54] and (iv) surface imprinting. 

Several selective interactions by MIP membrane systems have been reported. For example, an L-phenylalanine imprinted membrane prepared by in-situ crosslinking polymerization showed different fluxes for various amino acids [44]. Yoshikawa et al. [51] have prepared molecular imprinted membranes from a membrane material which bears a tetrapeptide residue (DIDE resin (7)), using the dry phase inversion procedure. It was found that a membrane which contains an oligopeptide residue from an L-amino acid and is imprinted with an L-amino acid derivative, recognizes the L-isomer in preference to the corresponding D-isomer, and vice versa. Exceptional difference in sorption selectivity between theophylline and caffeine was observed for poly(acrylonitrile-co-acrylic acid) blend membranes prepared by the wet phase inversion technique [53]. 

Those Warren-Cowley parameters have been determined in situ above the order-disorder transition temperature by diffuse neutron scattering. From these experimentally determined static correlations, the first nine effective pair interactions have been deduced using inverse Monte Carlo simulations. 

An interesting combination of enzymatic with non-enzymatic transformation in a one-pot three-step multiple sequence was reported by Waldmann and coworkers [82]. Phenols 125 in the presence of oxygen and enzyme tyrosinase are hydroxylated to catechols 126 which are then oxidized in situ to ortho quinones 127. These intermediates subsequently undergo a Diels-Alder reaction with inverse electron demand by reaction with different dienophiles (Table 4.19) to give endo bicyclic 1,2-diketones 128 and 129 in good yields. 

The mechanism of these reactions is usually Sn2 with inversion taking place at a chiral RX, though there is strong evidence that an SET mechanism is involved in certain cases, ° especially where the nucleophile is an a-nitro carbanion and/or the substrate contains a nitro or cyano group. Tertiary alkyl groups can be introduced by an SnI mechanism if the ZCH2Z compound (not the enolate ion) is treated with a tertiary carbocation generated in situ from an alcohol or alkyl halide and BF3 or AlCla, or with a tertiary alkyl perchlorate. ... 

By performing in situ the polymerization of acrylamide in water/AOT/toluene microemulsions, clear and stable inverse latexes of water-swollen polyacrylamide particles stabilized by AOT and dispersed in toluene have been found [192-194], It was shown that the final dispersions consist of two species of particles in equilibrium, surfactant-coated polymer particles (size about 400 A) with narrow size distribution and small AOT micelles (size about 30 A). 

Tocopheryl)propionic acid (50) is one of the rare examples that the o-QM 3 is involved in a direct synthesis rather than as a nonintentionally used intermediate or byproduct. ZnCl2-catalyzed, inverse hetero-Diels-Alder reaction between ortho-qui-none methide 3 and an excess of <2-methyl-C,<9-bis-(trimethylsilyl)ketene acetal provided the acid in fair yields (Fig. 6.37).67 The o-QM 3 was prepared in situ by thermal degradation of 5a-bromo-a-tocopherol (46). The primary cyclization product, an ortho-ester derivative, was not isolated, but immediately hydrolyzed to methyl 3-(5-tocopheryl)-2-trimethylsilyl-propionate, subsequently desilylated, and finally hydrolyzed into 50. 

In situ CO titration experiments have also been conducted on multicomposition systems, that is, inverse model catalyst. Schoiswohl et al. [68] in their studies compared the CO titration reaction on three surfaces clean Rh(l 1 1) surface, Rh (111) surface covered with large 2D V309 islands (mean size >50 nm), and Rh(l 11) surface covered with small 2D V309 islands (meansize<15 nm). Prior to CO titration, the three surfaces were exposed to 10-7 mbar 02 to form a (2 x l)-0 phase at room temperature. In situ STM was used to follow the titration reaction in the presence of 10 x-10 7 m liar CO. CO titration on the clean Rh(l 1 1) surface or the Rh(l 1 1) surface with large V309 islands exhibits similar reaction kinetics. Figure 3.19 shows... 

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