Organic Reactions Promoted by Non-Metallic Catalysts

Because the use of a stoichiometric amount of chromium-based oxidant is not desirable from the standpoint of green chemistry, a number of approaches to employ catalytic amount of oxidant in combination with a stoichiometric amount of reoxidant have been reported. 

Ruthenium derivatives have been used for oxidation reactions. Ley and co-workers reported a useful method for the oxidation of primary alcohols to aldehydes by means of catalytic amount of n-Pr4N + Ru04 (TPAP) in the presence of a stoichiometric amount of N-methylmorpholine oxide (Equation 10.2) [6]. 

Recently, Ishihara and co-workers developed a more powerful hypervalent iodine catalyst, generated in situ from 2-iodobenzoic acid and furthermore demonstrated that its sulfonic acid analog 2 is more reactive as a precatalyst (Equation 10.3) [8]. They reported that it was not necessary to isolate hypervalent iodine compounds, which are potentially explosive oxidants, and furthermore that more powerful oxidants could be generated in situ. 

Ishii and co-workers reported the N-hydroxyphthalimide (NHIP)-catalyzed nitro-sation of cyclohexane with te.it-butyl nitrite ( BuONO) to give nitrosocyclohexane in high yield (Equation 10.5) [11]. Subsequently, they reported an efficient one-pot procedure for the preparation of e-caprolactam from cyclohexane by means of cyanuric acid chloride [12]. The present route towards e-caprolactam obviates the use of corrosive NOC1 in the photonitrosation of cyclohexane. 

The Mukaiyama aldol reaction is an important and fundamental reaction for the preparation of polyols. Mukaiyama and co-workers reported that trityl salts are effective as catalysts for Michael reactions (Equation 10.6) and Mukaiyama aldol reactions (Equation 10.7) in addition to traditional Lewis acids such as TiCI4 and SnCl4 [13]. 

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