A Facile One‐Step Synthesis of 2‐Arylindazoles via Reductive Cyclization of N‐(2‐nitroarylidene)amines

A mild and efficient synthesis of 2‐arylindazole derivatives via the reductive cyclization of nitro‐aryl substrates mediated by a low‐valent titanium reagent (TiCl₄/Sm/Et₃N) has been developed. The attractive features of the current method include an N–N bond formation and the selective reduction of the C = N bond and nitro group, both of which were easily achieved in one‐pot by controlling the pH of the reaction mixture.     

Synthesis of Bis‐1,4‐Dihydropyridine Derivatives

Abstract

A series of bis‐1,4‐dihydropyridine derivatives were synthesized by the reaction of p‐phenylenedialdehyde or m‐phenylenedialdehyde and active methylene compounds.     

Biology-oriented synthesis of stereochemically diverse natural-product-derived compound collections by iterative allylations on a solid support

A strategy aiming at the introduction of stereocenters into polymer-bound natural-product-derived and -inspired compound collections is presented. Treatment of immobilized aldehydes with Brown's pinene-derived allylboranes results in the stereoselective formation of homoallylic alcohols with up to 89 % ee (ee=enantiomeric excess). Subsequent iterative ozonolysis-allylation sequences with up to three allylations on a solid support give access to 1,3-polyols with different relative configurations. Esterification with acryloyl chloride and final ring-closing metathesis yields alpha,beta-unsaturated delta-lactones with multiply oxygenated side chains, a substructure found in a group of natural products with a broad range of biological activity. The flexibility of the approach is exemplified by the parallel synthesis of all eight diastereomers of cryptocarya diacetate on a solid support. The individual isomers are obtained in overall yields of 40-60 % over 10 steps and with 63-85 % diastereoselectivity for the major isomer.     

Efficient Synthesis of Functionalized Thiazoles from Acid Chlorides,Tetramethylthiourea, Ethyl Bromopyruvate,and Ammonium Thiocyanate

An efficient synthesis of ethyl 2‐(dimethylamino)‐1,3‐thiazole‐4‐carboxylates is described via a four‐component reaction between acid chlorides, tetramethylthiourea, ethyl bromopyruvate, and ammonium thiocyanate.     

Preparation of o‐bromobenzophenone derivatives from lithium diarylcuprate(I) reagents

The reaction of lithium diarylcuprate(I) reagents with o‐bromobenzoyl chloride has been investigated. In general, the reaction proceeds well to give synthetically useful o‐bromobenzophenone derivatives as the major product. It is suggested that a minor substituent effect, whereby diarylcuprate reagents containing an ortho or meta substituent react more favourably, may be attributed to small changes in the structure of the organometallic reagent. Copyright © 2000 John Wiley & Sons, Ltd.     

Protecting‐Group‐Free Total Synthesis and Biological Investigation of Cabucine Oxindole A†

Owing to their challenging structures and promising biological profiles, spirooxindole alkaloids have long attracted much attention from the synthetic community. Herein, we wish to describe a concise, protecting‐group‐free total synthesis of cabucine oxindole A, a putative natural spirooxindole alkaloid and a possible biosynthetic congener of cabucine and palmirine. Key transformations of our approach include a one‐step, organocatalytic and enantioselective construction of the spiro[pyrrolidine‐3,3’‐oxindole] moiety and a Korte rearrangement to furnish the final dihydropyran motif. Biological investigation of 1 and its synthetic intermediates revealed lactone 2 as a mild MOLT‐4 and MCF7 cell line inhibitor.     

Biology‐Oriented Combined Solid‐ and Solution‐Phase Synthesis of a Macroline‐Like Compound Collection

Macrolines constitute a class of natural products that has more than 100 members and displays diverse biological activities. These compounds feature a cycloocta[b]indole scaffold that represents an interesting target structure for biology‐oriented synthesis (BIOS). We have presented a solid‐phase synthesis of isomerically pure cycloocta[b]indoles by employing the Pictet–Spengler reaction and the Dieckmann cyclization as key steps. The scope of this reaction sequence was investigated in more detail by using various additional diversification procedures, such as Pd‐catalyzed Sonogashira or Suzuki couplings on a solid phase, thus allowing, for example, the generation of 10‐substituted cycloocta[b]indole derivatives. Finally, solution‐phase decoration of the cycloocta[b]indole skeleton by reduction and saponification was evaluated, thereby further extending the scope of the solid‐phase synthesis.     

Synthesis and Herbicidal Activity of Novel N‐(2‐Fluoro‐5(3‐methyl‐2,6‐dioxo‐4‐(trifluoromethyl)‐2,3‐dihydro‐pyrimidin‐1(6H)‐yl)phenyl)‐2‐phenoxyacetamide Derivatives

Thirteen novel N‐(2‐fluoro‐5‐(3‐methyl‐2,6‐dioxo‐4‐(trifluoromethyl)‐2,3‐dihydropyrimidin‐1(6H)‐yl)phenyl)‐2‐phenoxy)acetamides were designed and synthesized utilizing 4‐fluoro‐aniline and ethyl 3‐amino‐4,4,4‐trifluoro‐but‐2‐enoate as starting materials. The chemical structures of all compounds were confirmed by ¹H NMR, IR, mass spectrum and elemental analyses. Subsequently, the herbicidal activities of the as‐prepared compounds were evaluated in the greenhouse. Bioassay results indicated that most of compounds had better herbicidal activities against dicotyledonous weeds. Among all the tested compounds, compounds 4a – 4i showed good herbicidal activities at both pre‐emergence and post‐emergence treatment against two or three kinds of dicotyledonous weeds, such as Abutilon theophrasti Medic, Amaranthus ascendens L, and Chenopodium album L at the dosage of 75 g ai/ha.     

Concise total synthesis of (-)-myxalamide A

The MIDA touch: A concise and highly convergent protecting-group-free total synthesis of (-)-myxalamide?A involves a stereoselective vinylogous Mukaiyama aldol reaction of a vinylketene silyl N,O-acetal, together with a one-pot Stille/Suzuki-Miyaura cross-coupling reaction using Burke's N-methyliminodiacetic acid (MIDA) boronate to connect left- and right-hand fragments of the molecule (see scheme).