Reactions Luche

Keywords aldehyde, ketone, halide, Reformatsky reaction, Luche reaction, Zn, NH4C1, /Miydroxy ester... 

Synthesis of (-I-) calanolide A (Scheme 8-11) was achieved by enzyme catalyzed resolution of the aldol products ( )-53. Compound 7 with acetaldehyde by aldol reaction in the presence of LDA/TiCU stereoselectively produced a mixmre of ( )-53 and ( )-54 (94% yield), the ratio of which was 96 4. ( )-53 was then resolved by lipase AK-catalyzed acylation reaction in the presence of tert-butyl methyl ether and vinyl acetate at 40 °C to obtain 41% yield of (+)-55 and 54% yield of the acetate (—)-56. Mitsunobu cyclization of (+)-55 in the presence of tri-phenylphosphine and dielthyl azodicarboxylate afforded 63% yield of (-l-)-43 with 94% ee as determined by chiral HPLC. Luche reaction on (+)-43 with CeCla 7H2O and triphenyl phosphine oxide and NaBH4 in the presence of ethanol at 30 °C gave the crude product. It was purified by column chromatography on silica gel to give 78% yield of a mixture containing 90% of (+)-calanolide A and 10% (+)-calanohde B, which were further separated by HPLC. 

Reformatsky and Luche reactions with Zn provide more economical C-C bond formation methods than Grignard reactions, which use more expensive Mg metal. Both the reactions proceed efficiently in the absence of solvent [10], These nonsolvent reactions can be carried out by a very simple procedure and give products in higher yield than with solvent. 

Luche reaction also proceeds efficiently in the absence of solvent [10]. Treatment of aldehydes, 21a, 21e, 25, 26, or ketones, 27, 28, with 3-bromopropene... 

Table 15-7. Reaction time and yields of the nonsolvent Luche reaction of aldehydes and ketones with 24.

This reaction was first reported by Luche in 1985. It is the modification of the initial aqueous allylation of carbonyl compounds (in 1983) via the intermediacy of tin in the presence of a catalytic amount of hydrobromic acid (HBr), to the zinc mediated allylation of carbonyl compounds using ultrasonic irradiation in saturated aqueous NH4CI/THF solution. Thus the new reaction condition is referred to as the Luche reaction. In parallel, Li" and Chan extended the Barbier-Grignard-type reaction to successfully proceed in aqueous media and contributed to the new area called green chemistry. ... 

Although the details of the mechanism are still under debate, the Luche reaction probably proceeds via radical mechanism, similar to that of Barbier-Grignard-type reaction occurring in aqueous solution, as outlined here. 

Other references related to the Luche reaction are cited in the literature. 

This reaction is related to the Aldol Condensation, Blaise Condensation, and Luche Reaction. 

Recent examples s. F. Fringuelli et al., Gazz. Chim. ItaL 779, 249 (1989) (Baeyer-Villiger oxidation) Synth. Meth. 27, 1H44 (Heck arylation) N.A. Bumagin et al., Izv. Akad. Nauk SSSR Ser. Khim. 1989, 2394 (boronic acid coupling) S.R. Wilson, M.E. Guazzaroni, J. Org. Chem. 54, 3087-91 (1989) (Luche reaction). 

Wilson and Guazzaroni (1989) devised a modification of the Luche reaction by using a solid organic phase, such as reverse-phase C-18 silica gel, instead of tetrahydrofuran as the cosolvent. The solid organic phase can be reused and disposal of the solvent after the reaction is environmentally safe. Unfortunately, the synlanti-selectmty was not improved regarding the Luche conditions. No chelation control was observed with p-alkoxyaldehydes. 

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