1,720,977 research outputs found
ChemInform Abstract: Cyclopropyl Building Blocks for Organic Synthesis. Part 148. A Convenient Access to Variously Substituted Spiro[cyclopropane‐1,4′‐oxazoline]s.
No full textA Convenient Access to Variously Substituted Spiro[cyclopropane‐1,4′‐oxazoline]s
No full textMichael additions of carboxamides 2a-d under basic conditions onto methyl 2-chloro-2-cyclopropylidene acetate (1) with subsequent ring closure furnished the 4-spirocyclopropanated methyl oxazolinecarboxylates 3a-d (51-81% yields), from which the corresponding free carboxylic acids 4a-d were obtained by hydrolysis in excellent yield (89-93 %). Coupling reactions of 4a-d with different o-hydroxyaniline derivatives in the presence of HOAt/EDC and 2,4,6-collidine gave the anilides 5 in good to very good yields (55-92 %). The latter under Mitsunobu reaction conditions (Ph(3)P/DEAD) furnished the benzoxazole derivatives 6 (81-88 %). The bromine substituent in the N-methylated 4-spirocyclopropanated 2-(bromophenyl)oxazoline-5-carboxanilides 8c,d were aminated with various secondary amines under Buchwald-Hartwig reaction conditions to give the 2-(aminophenyl)oxazolinecarboxanilides 9 (12-90 %). Suzuki cross-couplings of 8c with arene- and hetareneboronic acids provided the oxazolines with 2-biaryl substituents 10-13 (65-90 %). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
High yielding selective access to spirocyclopropanated 5-oxopiperazine-2-carboxylates and 1,4-diazepane-2,5-diones from methyl 2-chloro-2-cyclopropylideneacetate
No full textThe 2-spirocyclopropanated methyl 5-oxopiperazine-2-carboxylate 3 and the 3-spirocyclopropanated 6-chloro-1,4-diazepane-2,5-dione 4 could both be prepared at choice in 93 and 88% yield, respectively, from methyl 2-chloro-2-cyclopropylideneacetate (1) in a sequence of Michael addition of 3-benzyloxypropylamine, peptide coupling with N-Boc-glycine, Boc-group removal and cyclization. Transformation of the benzyloxypropyl side chain, peptide coupling with N-Boc-(S)-asparagine, deprotection and repeated cyclization led to the octahydro[2H]pyrazino[1,2-a]pyrazinetrione scaffold 10 containing a rigidified mimic of a tripeptide with a DGR motif The overall yield of 11 after deprotection of 10 (a total of 13 steps in 8 distinct operations) was 30%
ChemInform Abstract: Cyclopropyl Building Blocks in Organic Synthesis. Part 77. A New Highly Efficient Three-Component Domino Heck-Diels-Alder Reaction with Bicyclopropylidene: Rapid Access to Spiro[2,5]oct-4-ene Derivatives.
No full textFacile synthesis of structurally diverse 5-oxopiperazine-2-carboxylates as dipeptide mimics and templates
No full textA sequence of Michael addition of a primary amine onto methyl 2-chloro-2-cyclopropylidene-acetate (1), acylation of the adduct with alpha-bromo acid chlorides under modified Schotten-Baumann conditions and ring-closing twofold nucleophilic substitution on the thus formed bishalides 3a-e with aliphatic or aromatic amines according to a very simple protocol with final acid/base extraction or filtration over silica gel for purification leads to the 3-spirocyclopropanated 5-oxopiperazine-2-carboxylates 2 or in two cases, after intermolecular transesterification of 2, to bicyclic oxopiperazines 6, with a remarkable variability of the substituents R(1)-R(3) in 39-99% yields ( 20 examples). Starting with alpha-bromophenylacetic acid chloride, the trans-configured 6-phenyl-5-oxopiperazine-2-carboxylates are formed preferentially
ChemInform Abstract: Cyclopropyl Building Blocks in Organic Synthesis. Part 66. A New and Efficient Access to Thiazoline-4-carboxylates and Cysteine Derivatives Incorporating Cyclopropyl Groups.
No full textCyclopropyl Building Blocks for Organic Synthesis. Part 85. Facile Preparation and Chemical Transformations of Spirocyclopropane-Anellated Heterocycles.
No full textChemInform Abstract: Cyclopropyl Building Blocks in Organic Synthesis. Part 54. Nitrogen-Based Linkers. Part 6. New Efficient Multicomponent Reactions with C-C Coupling for Combinatorial Application in Liquid and on Solid Phase.
No full textMethyl 2‐(Benzyloxycarbonylamino)‐2‐cyclopropylideneacetate: A Versatile Building Block for Cyclopropyl‐Containing Amino Acids
No full textMethyl 2-(benzyloxycarbonylamino)-2-cyclopropylideneacetate (2) was prepared in nine steps starting from L-serine in an overall yield of 24 %. It has been demonstrated to be reasonably reactive in Michael additions of various nucleophiles (6 examples, 75-98%) yields) as well as Diels-Alder reactions, both leading to new cyclopropyl-containing amino acids in protected form. An application of 2 in the synthesis of methyl 4-tert-butoxycarbonylmethyl-5-oxo-4,7-diazaspiro-[2.5]octane-8-carboxylate (15), a precursor for geometrically constrained bicyclic peptidomimetics of type 16, has also been proved. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009
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