Thiourea polymer-bound

Schiff base thiourea catalysts (2 mol%) first enantioselective (polymer-bound) thioureas, Strecker reactions (92% yl. 91% ee)... 

Figure 6.15 Polymer-bound Schiff base thiourea catalyst 41 bearing 5-pivaloyl-substitution and its nonimmobilized urea analog 42 optimized for the asymmetric Strecker reaction of aromatic and aliphatic aldimines.

Scheme 6.43 Recycling study Polymer-bound Schiff-base thiourea 41 catalyzed the Strecker reaction of pivalaldimine without loss of activity or enantioselectivity even after 10 catalytic cycles.

Scheme 6.44 Reaction sequence for the synthesis of enantiopure (/ )-tert-leucine hydrochloride starting from the pivalaldimine Strecker adduct obtained under catalysis with polymer-bound thiourea 41.

Figure 6.19 Ester-functionalized thiourea 59, insoluble crosslinked polymer-bound thioureas (60 61) and soluble PEG-bound thiourea 62 screened in the asymmetric Michael addition of diethyl malonate to trarrs-P-nitrostyrene at rt in toluene (59, 60, and 61) and dichloromethane (62).

Methylisothiourea has also been used in place of thiourea to give 2-methylthio-5-cyanopyrimidinone derivatives <2006JME3988>, and polymer-bound thiouronium salts 733 have also been used to prepare derivatives 734 which can be displaced from the solid phase by oxidation of the sulfur atom to give sulfone 735, and subsequent displacement with amines <2002BML667> (Scheme 8). 

Also, polymer bound thioureas 29 are converted into carbodiimides 30 using Mukaiyama s reagent (2-chloro-l-methylpyridinium iodide) in the presence of triethy-lamine. This polymer is used in the solid phase synthesis of 2-aminoimidazolinones. °... 

Procedure for multicomponent reaction Polymer-bound thiouronium salt 111 was prepared under standard conditions [132] by reacting thiourea with Merrifield resin in DMF at 80 °C. Resin 111 (0.8 mmol was treated with ethyl cyanoacetate (8 mmol) and various substituted aromatic aldehydes (8 mmol) and K2CO3 (10 mmol) in DMF at 80 °C for 24 h, under shaking in an Advanced Chemtech (Advanced ChemTech, Inc., LouisviUe, KY,... 

Polymer-bound 5-(2-bromoacetyl)pyrroles could be converted into thiazolylpyrroles, aminothiazolylpyrroles and selenazolylpyrroles through Flantzsch-type reaction with thioamides, thioureas or selenourea respectively. The reaction conditions that were optimized for the three different types of building blocks are shown in Figure 6.16. 

The excess of 34 was trapped either with A (4-carboxyphenyl)thiourea (36) yielding 37 and removed by LPE, or with polymer-bound thiouronium salt 38 to yield polymer-bound imidazole 39 (in analogy to a liquid-phase strategy developed by Dodson et al. ) and removed by SPE. Subsequent treatment of thiazoles 35 with a series of amino acid-derived isocyanates 40 gave the second generation of thiazoles 41 in essentially quantitative yields. Excess of 40 was trapped with... 

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