New Routes to Heterocycles

The efficient constniction of substituted heterocycles is central to medicinal chemistry. Yoshinori Kondo of Tohoku University reports (J. Am. Chem. Soc. 125 8082, 2003) that the novel base 2 will, in the presence of Znl, and an aldehyde, deprotonate heterocycles, to give the hydroxyalkylated products 3 and 5. Benzene rings also participate - 6 is converted to 7. 

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The lithiation of methoxypyridazines (which, for 251, works even with BuLi) has been used to develop new routes to heterocyclic biaryls such as 252 (Scheme 124) . In the pyridazine series MeO turns out to be a stronger director than Cl, as expected . It also... 

The catalytic generation of alkynones and chalcones by palladium catalyzed reactions is an entry to sequential, consecutive, and domino transformations and opens new routes to heterocycles by consecutive coupling-cyclocondensation or Cl-cyclocon-densation sequences. The advantages are not only the compatibility of similar reaction conditions but also the tunable reaction design that allows the combination of several organic and organometallic elementary reactions to new diversity oriented syntheses. Future developments will address also sequentially catalyzed processes... 

New routes to heterocycles from unsaturated carbanions, heterocumulenes and thiocarbonyl compounds 01EJO4569. 

This sequence has been proposed as a novel approach to olefin separation and purification. Ffowever, there is disagreement about the reversibility of the reaction because it has been shown that irreversible reduction to the dianionic complex occurs through an ECE process.1082 A convenient new route to 1,2-enedithiolate complexes of Ni has been reported, which starts from the bisfhydrosulfldo) complex [Ni(dppe)(SFI)2] and various a-bromoketoues(heterocycle-C(0)CH2Br). 

The father of miinchnone chemistry, Rolf Huisgen, reported (130) the 1,3-dipolar cycloaddition of miinchnone 38 with p-nitrophenyldiazonium salt 226 to give the triazolium salt 227. This reaction would appear to be an important new route to these heterocycles. 

Five- and six-membered heterocycles, containing either a nitrogen or oxygen atom, and in particular pyrrolidine rings, are very important in natural products synthesis. There are many methods by which all these compounds may be synthesized and new routes to this target are constantly being sought. 

A new route to dichlorofluoromethyl substituted heterocycles, including the 1,4-naphtho[l,8a,8-e/]diazepin-2(l/f)-one 225, has been described based on the reaction of bifunctional nucleophiles with 3-chloropentafluoropropane-1,2-oxide [01JFC1]. 

Kim, G., Keum, G. A new route to quinolone and indole skeletons via ketone and ester-imide cyclodehydration reactions. Heterocycles 1997,45, 1979-1988. 

Tetrahydrofuranes.1 An example of a new route to these heterocycles is formulated in equation (I). Cyclization with acid alone is effected in only about 30%... 

New routes to ( + )-427 that employ the late-stage reductive cyclization of aminoketones continue to flourish. In Ae synthesis by Higasfaiyama et al, ketal 445 and (i )-A -benzylphenylglycinol 446 were condensed to form the chiral oxazolidine 447 (Scheme 55) 410). The heterocycle was cleaved diastereoselectively with pent-... 

Preparation of 5-amino-6-oxo-l,6-dihydro-1,2,4-triazine-3-carboxylic acid derivatives and the synthesis of compound libraries thereof have been reported <04TL2791>. Intramolecular inverse electron demand Diels-Alder reactions of imidazoles with 1,2,4-triazines have been described as a new route to obtain l,2,3,4-tetrahydro-l,5-naphthyridines and related heterocycles... 

One method for the a-iodination of ketones calls for the assistance of selenium dioxide. Heterocyclization. A new route to a-iodo boronic acids consists of iodoethe-rification. p-Iodobutenolides that are useful for carbon chain extension at the P-position (via Pd-catalyzed coupling) are readily accessible by iodolactonization of allenic acids ... 

Kvi cala, J. Hovorkova, P Paleta, O. Reactions of 3-chloropentafluoropropene-l,2-oxide with bifunctional nucleophiles a new route to chlorodifluoromethyl-substituted heterocycles. J. Fluorine Chem. 2001, 108, 1. 

Elimination of a heteroatom bridge. A new route to condensed heterocycles is illustrated for synthesis of 4-carboethoxyoxindole (2) from the Diels-Alder adduct (1) of N-acetylpyrrole and 1,3-dicarboethoxyaIlene. Treatment of 1 with COOCsHe... 

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