Yoshinori Nishii

Direct, practical, and powerful crossed aldol additions between ketones and ketones or aldehydes utilizing environmentally benign TiCl4–Bu3N reagent

Abstract An efficient TiCl4–Bu3N—(cat. TMSCl)-promoted aldol addition between ketones and ketones or aldehydes was performed. This environmentally benign method is advantageous from a green chemical viewpoint with regard to yield, substrates variation, reagent availability, and simple procedures. This method was applied to a short step formal synthesis of (R)-muscone, a natural macrocyclic musk.

Novel and efficient method for esterification, amidation between carboxylic acids and equimolar amounts of alcohols, and amines utilizing Me2NSO2Cl and N,N-dimethylamines; its application to the synthesis of coumaperine, a natural chemopreventive dieneamide

Abstract Various carboxylic esters or amides were prepared in good to excellent yield between carboxylic acids and equimolar amounts of alcohols or amines under very mild conditions (0–45°C; within 3 h) using dimethylsulfamoyl chloride (Me 2 NSO 2 Cl; 1 ) combined with N , N -dimethylamines (Me 2 NR: 2a ; R=Me, 2b ; R=Bu). The choice of the sulfamoyl chloride and the amine is crucial for the reaction; that is, sterically uncrowded amines accelerated the present esterification and amidation. This agent had some advantages over methanesulfonyl chloride ( 3 )/amines as for the atom-economy, avoidance of side reactions, and had very high chemoselectivity toward the carboxyl group vs the hydroxyl group; the experiment was performed by the addition of 1 to the mixture of carboxylic acids and alcohols. Application of this method to the synthesis of coumaperine, a chemopreventive natural product, was performed using the present amidation as a key step.

Synthesis and stereostructure–activity relationship of three asymmetric center pyrethroids: 2-methyl-3-phenylcyclopropyl-methyl 3-phenoxybenzyl ether and cyanohydrin ester

2-Methyl-3-phenylcyclopropylmethyl 3-phenoxybenzyl ether 2 and cyanohydrin ester 3, a couple of pyrethroids with three asymmetric centers, were synthesized. Of each of the four diastereomers of 2 and 3, only the (1R*,2R*,3R*)-2a and 3a showed significant insecticidal activities. Dual sets of enantiomers [(1R,2R,3R)-(-)-2a and (1S,2S,3S)-(+)-2a] and [(1R,2R,3R)-(-)-3a and (1S,2S,3S)-(+)-3a] were synthesized through the asymmetric cyclopropanation using the Aratani catalyst. Significant separations of insecticidal activities were observed between both the enantiomers against the tobacco cutworm (Spodoptera litura) and the common mosquito (Culex pipiens pallens); (1S,2S,3S)-(+)-2a and (+)-3a showed higher activities than their antipodes (1R,2R,3R)(-)-2a and (-)-3a. This result is the second example of such synthetic pyrethroids with three asymmetric centers.

Total synthesis of pederin, a potent insect toxin: the efficient synthesis of the right half, (+)-benzoylpedamide

Abstract A simple and efficient synthesis of (+)-benzoylpedamide, the right half of pederin, was achieved in 16 steps with a 35% overall yield from ( S )-malic acid. The key steps include the SmI 2 -mediated intramolecular Reformatsky reaction, stereoselective allylation, the Sharpless asymmetric dihydroxylation, and amidation. The total synthesis of pederin was accomplished via coupling of the left and right halves.

Efficient one-step synthesis of trialkylsubstituted 2(5H)-furanones utilizing direct Ti-crossed aldol condensation and its application to the straightforward synthesis of (R)-mintlactone and (R)-menthofuranElectronic supplementary information (ESI) available: calculated structures of 7 and 8. See http://www.rsc.org/suppdata/cc/b2/b208077j/

TiCl4–Bu3N-mediated condensation of ketones with α,α-dimethoxyketones afforded trialkylsubstituted 2(5H)-furanones in a one-pot manner, wherein aldol addition and furanone formation occurred sequentially; its application to straightforward synthesis of (R)-mintlactone and (R)-menthofuran, two representative natural mint perfumes, is demonstrated.

SmI2-promoted Reformatsky-type reaction and acylation of alkyl 1-chlorocyclopropanecarboxylates.

In the presence of HMPA in THF, highly stereoselective SmI(2)-promoted substitutions of alkyl 1-chlorocyclopropanecarboxylates 1 using various ketones, aldehydes (Reformatsky-type reaction), and acyl chlorides (acylation) proceeded to give trans-adducts (2 or 5) in good to high yield with excellent trans-stereoselectivity (trans-add/cis-add = > 99/1). The Reformatsky-type reaction of 1 with aldehydes and unsymmetrical ketones proceeded with moderate diastereoselectivity (re-face-adduct/si-face-adduct = 60/40-75/25).

Sequential and regioselective Friedel-Crafts reactions of gem-dihalocyclopropanecarbonyl chlorides with benzenes for the synthesis of 4-aryl-l-naphthol derivatives

Novel, sequential and regioselective Friedel–Crafts type reactions of (E)-3-aryl-2,2-dihalogenocyclopropanecarbonyl chlorides 1 and 2,2-dichlorocyclopropanecarbonyl chlorides 3 with benzenes produce various 4-aryl-3-halogeno-1-naphthols 2 and 4-aryl-1-naphthols 4, respectively. One of the benzannulations involves the intramolecular cyclization of acid chlorides 1, followed by intermolecular coupling with substituted benzenes to give 4-aryl-3-halogeno-1-naphthols 2. As a demonstration of this annulation, 4-aryl-3-bromo-1-naphthols 2i and 2k are successfully converted into new analogues of 1-aryl-3-hydroxymethyl-4-methoxy-2-naphthoic acid lactones 13, a class of lignan lactones. The other benzannulation involves three series of reactions using acid chlorides 3a–c: (1) the intermolecular Friedel–Crafts acylation of 3 with one benzene molecule giving the intermediary 2,2-dichlorocyclopropyl(phenyl)methanones 14a–c; (2) the intermolecular trapping of 14a–c with another benzene molecule accompanied by regioselective ring opening; and (3) the final intramolecular cyclization giving 4-phenyl-1-naphthols 4a–c. The use of p-xylene also gives the corresponding 4-(p-xylyl)-1-naphthol 4d. The reactions of alternatively prepared ketones 14 with benzenes gives a variety of ‘unsymmetrically’ substituted 4-aryl-1-naphthols 4c,e–k under identical conditions. However, the reaction using p-methoxyphenyl ketone analogues 14g does not produce 4-aryl-1-naphthols, but gives 5-aryl-2-(p-methoxyphenyl)-3-methylfurans 16. These annulations proceed straightforwardly (in a one-pot manner) and this variation is due to the highly regioselective cyclopropane ring-openings.

Synthesis and stereostructure–activity relationship of a synthetic pyrethroid, 2-chloro-1-methyl-3-phenylcyclopropylmethyl-3-phenoxybenzyl ether

Of the four diastereoisomers of 2-chloro-1-methyl-3-phenylcyclopropylmethyl 3-phenoxybenzyl ether 5, a new type of synthetic pyrethroid, which have been synthesized, only the (1R*,2S*,3S*)-isomer 5a showed significant insecticidal activity against the tobacco cutworm and the common mosquito. Two enantiomers (1R,2S,3S)-(–)-5a and (1S,2R,3R)-(+)-5a were prepared by the optical resolution process, and their absolute configurations were determined by chemical derivatization via predictable asymmetric cyclopropanation. Bioassay showed that the (1R,2S,3S)-(–)-5a was active, while (1S,2R,3R)-(–)-5a was not. The geometry around the asymmetric centre of the (1R,2S,3S)-enantiomer was correlated with that of representative pyrethroids which are both optically active and have insecticidal activity.

Novel method for the synthesis of α- and β-halogenonaphthalenes by regioselective benzannulation of aryl(gem-dihalogenocyclopropyl)methanols: application to the total synthesis of the lignan lactones, justicidin E and taiwanin C1

Acid treatment of two types of aryl(gem-dihalogenocyclopropyl)methanols (ADCMs) 1 and 3 gives α- and β-halogenonaphthalenes in good yields with excellent selectivity. These alternative annulations involve two distinctive types of highly regioselective acid-induced cyclopropane ring cleavage, wherein the preferential formation of more stable cationic intermediates determines the selectivity. The stereochemical mode of both the preparation and the annulation between diastereoisomers of an ADCM has been checked. As a demonstration of this annulation, a total synthesis of each of the natural lignan lactones, justicidin E 19 and taiwanin C 20, has also been performed. Since these 4-arylnaphthalenes are expected to exhibit biological activity, the anti-platelet activating factor (anti-PAF) activity of justicidin E has been assayed.

Regiocontrolled benzannulation of diaryl(gem-dichlorocyclopropyl)methanols for the synthesis of “unsymmetrically” substituted α-arylnaphthalenes

Abstract Aryl1(aryl2)(gem-dichlorocyclopropyl)methanols 1 underwent alternative benzannulation to give “unsymmetrically” substituted 1-(aryl1)-4-chloronaphthalenes 2/A catalyzed by SnCl4 or TiCl4 and to give 1-(aryl2)-4-chloronaphthalenes 2/B catalyzed by silyl triflates with good to excellent selectivities.