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Despite the limited success of copper-catalyzed alkylations, (NNS)CuCl proved to be an effective catalyst for the sp3 C–H alkylation of fluorene with alcohols. Various primary alcohols and challenging secondary alcohols were successfully used. The practical applicability of the method was effectively tested with several post-functionalization reactions. This copper-catalyzed alkylation of fluorene involved a borrowing hydrogen mechanism. [ABSTRACT FROM AUTHOR]

Despite the limited success of copper-catalyzed alkylations, (NNS)CuCl proved to be an effective catalyst for the sp 3 C-H alkylation of fluorene with alcohols. Various primary alcohols and challenging secondary alcohols were successfully used. The practical applicability of the method was effectively tested with several post-functionalization reactions. This copper-catalyzed alkylation of fluorene involved a borrowing hydrogen mechanism.

The utilization of earth-abundant, cheap, and nontoxic transition metals in important catalytic transformations is essential for sustainable development, and iron has gained significant attention as the most abundant transition metal. A mixture of FeCl 2 (3 mol %), phenanthroline (6 mol %), and KO t Bu (0.4 eqivalent) was used as an effective catalyst for the sp 3 C-H alkylation of fluorene using alcohol as a nonhazardous alkylating partner, and eco-friendly water was formed as the only byproduct. The substrate scope includes a wide range of substituted fluorenes and substituted benzyl alcohols. The reaction is equally effective with challenging secondary alcohols and unactivated aliphatic alcohols. Selective mono-C9-alkylation of fluorenes with alcohols yielded the corresponding products in good isolated yields. Various postfunctionalizations of C-9 alkylated fluorene products were performed to establish the practical utility of this catalytic alkylation. Control experiments suggested a homogeneous reaction path involving borrowing hydrogen mechanism with the formation and subsequent reduction of 9-alkylidene fluorene intermediate.

The utilization of economical and environmentally benign transition metals in crucial catalytic processes is pivotal for sustainable advancement in synthetic organic chemistry. Iron, as the most abundant transition metal in the Earth's crust, has gained significant attention for this purpose. A combination of FeCl 2 (5 mol%) in the presence of phenanthroline (10 mol%) and NaO t Bu (1.5 equivalent) proved effective for the C (α)-alkylation of oxindole, employing challenging secondary alcohol as a non-hazardous alkylating agent. The C (α)-alkylation of oxindole was optimized in green solvent or under neat conditions. The substrate scope encompasses a broad array of substituted oxindoles with various secondary alcohols. Further post-functionalization of the C (α)-alkylated oxindole products demonstrated the practical utility of this catalytic alkylation. One-pot C-H hydroxylation of alkylated oxindoles yielded 3-alkyl-3-hydroxy-2-oxindoles using air as the most sustainable oxidant. Low E -factors (3.61 to 4.19) and good Eco-scale scores (74 to 76) of these sustainable catalytic protocols for the alkylation and one-pot sequential alkylation-hydroxylation of oxindoles demonstrated minimum waste generation. Plausible catalytic paths are proposed on the basis of past reports and control experiments, which suggested that a borrowing hydrogen pathway is involved in this alkylation.