Stoermer reaction, Rap

Aldehyde Reagent Reaction temperature (°C) Product Yield (%) 

Secondly, the reaction of 89a, 90a, and K2CO3 under solvent-free conditions was monitored by IR spectral measurement. A mixture of 89a, an equimolar amount of 90a, and twice the molar amount of K2CO3 initially showed vC=0 absorption (C) at 1670 cm assigned to the formation of 93 this absorption decreased gradually and new vC=0 absorption bands appeared at 1696 (D) and 1641 cm (E) (Fig. 2). After 60 min, the C absorption band disappeared and the D and E absorptions increased. After further reaction at 80 °C for 10 min, the D absorption disappeared and only the E absorption remained in the spectrum (VI in Fig. 2). The spectrum VI is identical to that of the final product 91a. The appearance of the D absorption band together with a strong OH absorption band at 3465 cm suggests production of a ketoalcohol intermediate. 

In order to isolate the ketoalcohol intermediate, the following experiment was carried out. A mixture of 89a (1 g, 8.2 mmol), 90a (0.77 g, 5 mmol), and K2CO3 (1.38 g, 10 mmol) was stored at room temperature for 3 h,and the crude reaction product was added to a 1 1 mixture of ether and water. From the ether solution, c/s-2-benzoyl-3-hydroxy-2,3-dihydrobenzofuran (96) was obtained (0.18 g, 15% yield). Compound 96 showed its vC=0 absorption at 1696 cm k 

The cis configuration of 96 was elucidated by X-ray structure analysis. The data suggest that the cyclization reaction of the anion 95 generated from 94 to 91a proceeds stereoselectively in the solid state [16]. 

1 IR spectra of a mixture of 89a and twice the molar amount of K2CO3 in Nujol mulls. I Pure 89a for reference II1 min after mixing III 10 min after mixing 

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Rap-Stoermer reactions are useful for the preparation of 2-benzoylbenzofuran derivatives (91) by a base-assisted condensation of salicylaldehydes (89) with phenacyl bromides (90) (Scheme 15). However, these reactions are not very... 

In order to clarify the reason why the Rap-Stoermer reaction proceeds so efficiently under solvent-free conditions, the K2C03-assisted reaction of 89a and 90a was studied by IR spectral monitoring in Nujol mulls [ 16]. Firstly, the potassium salt formation of 89a was studied (Scheme 16). One minute after mixing of 89a with twice the molar amount of K2CO3, a vC=0 absorption band (B) appeared at 1692 cm" (spectrum II in Fig. 1), although 89a itself shows vC=0 absorption (A) at 1664 cm (spectrum I in Fig. 1). After 10 min, B disappeared and a new vC=0 absorption band (C) appeared at 1670 cm (spectrum III in... 

Table 12 K2C03-assisted solvent-free Rap-Stoermer reaction (1 h)...

Heating of 96 under solvent-free Rap-Stoermer reaction conditions easily gave 91a [16] (Scheme 16). 

Ethyl 3-aminofuropyridine-2-carboxylates were reported to be made either from 1-hydroxy-2-cyano-substituted pyridines and ethyl bromoacetate or from l-chloro-2-cyano-substituted pyridines and ethyl glycolate under microwave conditions <07S3247>. Microwave irradiation was also applied in the Rap-Stoermer reaction for the formation of benzo[A] furans from salicylaldehydes and diverse phenacyl bromides and phenacyl iodides... 

It has been shown that microwave irradiation gives improved yields in the Rap-Stoermer reaction of salicylaldehydes with diverse phenacyl bromides and iodides (Equation 119) <2007TL431>. 

Keywords Rap-Stoermer reaction, salicylaldehyde, phenacyl bromide... 

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