Weinreb amide based synthetic equivalents for convenient access to 4-aryl-1,2,3,4-tetrahydroisoquinolines

New synthetic equivalents, N-methoxy-N-methyl-N′-phenylsulfonyl glycinamide and N-methoxy-N-methyl-N′-benzyl-N′-tert-butyloxy carbonyl glycinamide based on WA functionality were developed for the convenient synthesis of 4-aryl-1,2,3,4-tetrahydroisoquinoline framework. Two simple reactions, N-benzylation and addition of arylmagnesium halide on the WA functionality of the former afforded the key intermediate for convenient synthesis of N-phenylsulfonyl protected 4-aryl-1,2,3,4-tetrahydroisoquinoline, through reduction and acid promoted cyclization. With the latter, the addition of arylmagnesium halide on the WA functionality followed by the same protocol afforded the direct synthesis of 4-aryl-1,2,3,4-tetrahydroisoquinolines in good yields. The acid promoted cyclization step enabled concomitant removal of N-Boc protection.     

Investigation of the scope of a [3+2] cycloaddition approach to isoxazole boronic esters

The [3+2] cycloaddition reaction of nitrile oxides and alkynylboronates provides direct access to a wide variety of isoxazole boronic esters. Specifically, this technique has been employed to generate trisubstituted isoxazole 4-boronates and disubstituted isoxazoles where the boronic ester moiety can be installed at C-4 or C-5 with high levels of regiocontrol. The application of this methodology in the synthesis of non-steroidal antiinflammatory agents is also described.     

A convenient synthetic approach to dioncoquinone B and related compounds

A total synthesis of dioncoquinone B and related compounds, including ancistroquinones B, C and malvon A, is presented. The strategy is based on available reagents and can be used as a preparative synthesis of a number of natural and synthetic biologically active (3-alkyl)-2,7,8-di(tri)methoxy(hydroxy)-1,4-naphthoquinones.     

Alkyl-substituted poly(2,5-benzophenone)s synthesized via Ni(0)-catalyzed coupling of aromatic dichlorides and their miscible blends

High molecular weight poly(2,5-benzophenone) derivatives were prepared by Ni(0)-catalyzed coupling of 4′-substituted 2,5-dichlorobenzophenones. Monomers were synthesized by the Friedel–Crafts reaction of 2,5-dichlorobenzoyl chloride and alkyl-substituted benzenes in the presence of aluminum chloride. The resulting polymers are soluble and show no evidence of crystallinity by DSC. Number average molecular weights are in the range of 9.2 × 10³–11.7 × 10³ g/mol by multiple angle laser light scattering (MALLS). Molecular weights obtained by MALLS are only slightly lower (∼90%) than those obtained by GPC (polystyrene standards). These polymers exhibit high thermal stability with glass transition temperatures ranging from 173 to 225°C and weight loss occurring above 450°C in nitrogen and 430°C in air. Additionally, the polymers were blended and the resulting polymer films appear to be miscible by DSC results. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2611–2618, 1998     

A convenient synthetic route to a useful synthon: 4-bromo-2-pyridinecarboxaldehyde

We have developed a novel four-step method to synthesise 4-bromo-2-pyridinecarboxaldehyde, from 2-picoline-N-oxide via 4-nitro-2-pyridinecarboxaldehyde, under mild reaction conditions.     

A convenient synthetic approach to alpha-amino-beta-lactam synthesis promoted by phenyl dichlorophosphate reagent

The ready and economical phenyl dichlorophosphate, in contrast to many reagents developed for activating carboxyl groups for the beta-lactam synthesis, is shown to be very efficient for the synthesis of alpha-vinylamino-beta-lactams from Dane salts and Schiff bases. Some observations toward the scope of the method are also briefly described. The interaction of acetic acids with ethanolimines afforded beta-lactams and/or oxazolidines according to the synthetic methodology used.     

Pd-catalyzed addition of boronic acids to vinylogous imines: a convenient approach to 3-sec-alkyl substituted indoles

A convenient approach to 3-sec-alkyl substituted indoles was developed via palladium-catalyzed addition of arylboronic acids to vinylogous imines generated in situ from sulfonylindoles under mild conditions.     

Development of a convenient synthetic route to aminochromenes via Buchwald C-N coupling

A convenient new synthetic route to p-aminophenylaminobenzo- and naphthopyrans was developed via palladium-catalyzed C-N coupling. It was demonstrated that novel targeted aminoderivatives reveal photochromic properties. The structure of intermediate p-nitrophenylaminochromenes was confirmed by X-ray crystallographic analysis.     

Highly chemoselective reduction of azides to amines by Fe(0) nanoparticles in water at room temperature

A highly chemoselective reduction of aryl, heteroaryl, acyl and sulfonyl azides to the corresponding amines has been achieved by Fe(0) nanoparticles in water at room temperature in the absence of external hydride source. Several readily reducible functionalities including alkene, alkyne, S-S linkage, OTBDMS remain unaffected during reduction.     

New synthetic approach to 8-allyltheophylline

Summary The synthesis of 8-allyltheophylline (8) from 5,6-diamino-1,3-dimethyluracil (1) and 3-butenoic acid byTraube's methodvia 6-amino-5-(3-butenoylamino)-1,3-dimethyluracil (2) failed because an attempted alkaline cyclization of the intermediate2 afforded (E)-8-(1-propenyl)-theophylline (3) under rearrangement of the terminal C=C bond. Therefore, the cyclodehydratation of 6-(3-butenylamino)-5-nitroso-1,3-dimethyluracil (7), available from 6-chloro-1,3-dimethyluracil (5)via 6-(3-butenylamino) derivative6 has to be used for obtaining the required product8.

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Ein neuer synthetischer Zugang zu 8-Allyltheophyllin

Zusammenfassung 8-Allyltheophyllin (8) kann nicht mittels derTraube-Synthese aus 5,6-Diamino-1,3-dimethyluracil und 3-Butensäurevia 6-Amino-5-(3-butenoylamino)-1,3-dimethyluracil (2) hergestellt werden, wei bei der alkalischen Cyclisierung des Zwischenproduktes2 Umlagerung der terminalen C=C-Doppelbindung unter Bildung von (E)-8-(1-Propenyl)theophyllin (3) erfolgt. Zur Darstellung der Verbindung8 muss man daher die Dehydratationscyclisierung von 6-(3-Butenylamino)-5-nitroso-1,3-dimethyluracil (7) anwenden. Letzteres ist aus 6-Chloro-1,3-dimethyluracil über das 6-(3-Butenylamino)-Derivat6 zugänglich.

     

A convenient cross-metathesis approach to trisporins

Three series of trisporins have been prepared using a strategy in which a cross-metathesis is the key step. This reaction has proved to be highly regioselective, allowing the combination of α- or β-ionone derivatives having a 1,1-disustituted olefin with trisubstituted alkenes. The stereochemistry of the newly formed olefins has been established by spectroscopic means.     

Reactions of 5,8-dichloro-2,3-dicyanoquinoxaline with amines and hydrazines. A new and efficient synthetic approach to 3-amino-5,8-dichloroflavazoles

Reactions of 5,8-dichloro-2,3-dicyanoquinoxaline with primary amines and hydrazines under different experimental conditions were investigated. Alkylamines provided novel 3-alkylamino-5,8-dichloro-2-cyanoquinoxalines and N-alkyl-(5,8-dichloro-3-alkylamino-2-quinoxalinyl)carboxamidines in high yields. Alkylhydrazines and lithium arylhydrazinides gave previously unattainable 1-alkyl-3-amino-5,8-dichloroflavazoles and 3-amino-1-aryl-5,8-dichloroflavazoles in good to near quantitative yields whose molecular structure was confirmed by X-ray crystallography of 3-[N,N-bis(4-chlorobenzoyl)amino]-5,8-dichloro-1-phenylflavazole. Reaction with hydrazine gave 5,8-dichloro-3-hydrazino-2-quinoxalinylcarboxamidrazone quantitatively, which was converted to the parent compound of this class of flavazoles, 3-amino-5,8-dichloroflavazole, in high yield by a pyrolytic process involving loss of hydrazine.     

A convenient synthetic approach to derivatives of 5-phenylsulfonyl-2-thiouracil and its condensed analogs

3-Amino-2-phenylsulfonylacrylonitrile, an available multicenter reagent, when treated successively with phenyl, ethyl, or allyl isothiocyanate and hydrochloric acid forms N³-substituted 5-phenylsulfonylthiouracils. Some of them were found to be suitable starting mateials for preparing of thiazoline and thiodiazolidine structures fused with the 4-pyrimidone system.     

A novel synthetic protocol for poly(fluorenylenevinylene)s: a cascade Suzuki-Heck reaction

This article reports the use of a cascade Suzuki-Heck reaction for the polymerization of suitable aryldibromides with potassium vinyltrifluoroborate resulting in the synthesis of a series of poly(fluorenylenevinylene)s. The protocol is characterized by a great versatility, deriving from the use of easily attainable substrates, and yields polymers with low percentages of structural 1,1-diarylenevinylene defects.     

A convenient 1,3-dipolar cycloaddition approach to pyridylpyrroles

A variety of 2-, 3-, and 4-pyridylpyrroles were synthesized in good to excellent yields via the 1,3-dipolar cycloaddition of symmetrical and unsymmetrical münchnones and nitroalkenes. The unsymmetrical münchnones show moderate to excellent regioselectivity.     

A synthetic approach to enfumafungin

The stereospecific synthesis of the dienophile subunits 5 was achieved from the butenolide 6. Ester 19 was obtained in 67% overall yield (2 steps), with no intermediate purification, by a sodium chlorite oxidation of the corresponding aldehyde in buffered conditions, followed immediately after extraction, by a Mitsunobu reaction of the relatively labile acid 3 with alcohol 13. The synthesis of the α,β-unsaturated aldehydes 22 and 23 is also reported. Tentative IMDA reactions of 22 and 23 were examined in thermal conditions, or with a Lewis acid catalysis, and results are reported herein.     

A Comparative Study of the Relative Stability of Representative Chiral and Achiral Boronic Esters Employing Transesterification

Summary. A comparative study of the transesterification of five representative chiral and achiral boronic esters with various structurally modified diols was undertaken to qualitatively understand the factors influencing the relative stability of these boronic esters. Several factors such as chelation, conformation, steric bulk of the substituents, size of the heterocycle, and entropy influence the relative rate of transesterification as well as the stability of the boronic esters. Amongst these boronic esters, pinanediol phenylboronic ester was found to be the most stable boronic ester whereas DIPT boronic ester appeared to be thermodynamically the least stable one. The transesterification with sterically hindered diols was observed to be relatively slow, but afforded thermodynamically more stable boronic esters. Boronic esters derived from cis-cyclopentanediols and the bicyclo[2.2.1]heptane-exo,exo-2,3-diols are relatively more stable. This study not only presents the qualitative picture of relative stability of various boronic esters, but also provides helpful hints regarding the possible recovery of chiral auxiliaries. Many C ₂-symmetric chiral auxiliaries, such as 2,3-butanediol, 2,4-pentanediol, DIPT, and cis-cyclohexane-1,2-diol, can be retrieved by simple transesterification of the corresponding boronic esters with commercial inexpensive diols, such as pinacol, 1,3-propanediol, and neopentyl glycol. This paper is dedicated to the memory of my mentor, the late Professor Herbert C. Brown (1912–2004). Professor Herbert C. Brown deceased on December 19, 2004. The work described herein was carried out at Purdue University during my stay as a post-doctoral research associate