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Despite the biological interest in chromane derivatives, few studies dedicated to the functionalisation of this heterocycle have been reported. Herein, our objective is to demonstrate the potential of alkali metal bases for the introduction of substituents at its positions 4 and 8, and to explain the observed reactivity based on quantum chemical calculations. Guided by these theoretical results, preliminary optimisation was carried out on 2,3‐dihydrobenzofuran before applying the optimal conditions to chromane. Deprotolithiation at C8 was thus achieved using n‐butyllithium in hexane at room temperature, while functionalisation at C4 was promoted by a 1:1 mixture of lithium 2,2,6,6‐tetramethylpiperidide and potassium tert‐butoxide in tetrahydrofuran at −50 °C. Various electrophiles were used to intercept the lithiated intermediates, providing a convenient access to substituted chromane derivatives. [ABSTRACT FROM AUTHOR]

With the aim of synthesizing biaryl compounds, several aromatic iodides were prepared by the deprotonative metalation of methoxybenzenes, 3-substituted naphthalenes, isoquinoline, and methoxypyridines by using a mixed lithium/zinc-TMP (TMP=2,2,6,6-tetramethylpiperidino) base and subsequent iodolysis. The halides thus obtained, as well as commercial compounds, were cross-coupled under palladium catalysis (e.g., Suzuki coupling with 2,4-dimethoxy-5-pyrimidylboronic acid) to afford various representative biaryl compounds. Deprotometalation of the latter compounds was performed by using the lithium/zinc-TMP base and evaluated by subsequent iodolysis. The outcome of these reactions has been discussed in light of the CH acidities of these substrates, as determined in THF solution by using the DFT B3LYP method. Except for in the presence of decidedly lower p Ka values, the regioselectivities of the deprotometalation reactions tend to be governed by nearby coordinating atoms rather than by site acidities. In particular, azine and diazine nitrogen atoms have been shown to be efficient in inducing the reactions with the lithium/zinc-TMP base at adjacent sites (e.g., by using 1-(2-methoxyphenyl)isoquinoline, 4-(2,5-dimethoxyphenyl)-3-methoxypyridine, or 5-(2,5-dimethoxyphenyl)-2,4-dimethoxypyrimidine as the substrate), a behavior that has already been observed upon treatment with lithium amides under kinetic conditions. Finally, the iodinated biaryl derivatives were involved in palladium-catalyzed reactions. [ABSTRACT FROM AUTHOR]

A series of methoxy- and fluoro-pyridines have been deprotometalated in tetrahydrofuran at room temperature by using a mixed lithium–zinc combination obtained from ZnCl 2 ·TMEDA (TMEDA= N , N , N ′, N ′-tetramethylethylenediamine) and LiTMP (TMP=2,2,6,6-tetramethylpiperidino) in a 1:3 ratio, and the metalated species intercepted by iodine. Efficient functionalization at the 3 position was observed from 4-methoxy, 2-methoxy, 2,6-dimethoxy, 2-fluoro and 2,6-difluoropyridine, and at the 4 position from 3-methoxy and 2,3-dimethoxypyridine. Interestingly, clean dideprotonation was noted from 3-fluoropyridine (at C2 and C4) and 2,6-difluoropyridine (at C3 and C5). The obtained regioselectivities have been discussed in light of the CH acidities of the substrates, determined both in the gas phase (DFT B3LYP and G3MP2B3 levels) and in THF solution. In the case of methoxypyridines, the p K a values have also been calculated for complexes with LiCl and LiTMP. [ABSTRACT FROM AUTHOR]