The synthesis of the isomeric components of San Jose scale pheromone — an illustration of a stereospecific synthesis of trisubstituted alkenes

Abstract

The three isomeric components of the San Jose scale pheromone, 5-7, have been synthesized from a common P-keto ester intermediate. A study of the alkylation of the dianion of methyl acetoacetate with a series of alkylating agents with the same carbon skeleton has been carried out. The trisubstituted alkenes in 5 and 6 have been synthesized stereospecifically via a copper-catalyzed coupling of a methyl Grignard reagent with the E or Z en01 phosphate from the alkylated P-keto ester. In the case of the Z en01 derivative, the coupling reaction was carried out on the diethyl-and diphenylphosphates, and the en01 triflate. 'The diethyl en01 phosphate gave the highest stereoselectivity. The synthetic pheromones were attractive to San Jose scale in the field.MARGOT ALDERDICE, CLAUDE SPINO et LARRY WEILER. Can. J. Chem. 71, 1955Chem. 71, (1993. Utilisant un p-ceto ester commun comme intermediaire, on a synthetise les trois isomitres 5-7 de la pheromone du pou de San JosC. On a rCalisC une Ctude de I'alkylation du dianion de 1'acCtoacetate de mCthyle par une sCrie d'agents d'alcoylation ayant le m&me squelette carbone. On a synthCtisC les alcitnes trisubstituCs 5 et 6 d'une maniitre stCreospCcifique en faisant appel a un couplage catalysC par le cuivre d'un mCthyl magnesien avec le phosphate d'Cnol E ou Z obtenu B partir du p-ceto ester alcoyle. Dans le cas du dCrivC Cnolique Z, on a rCalisC la reaction de couplage sur les phosphates Cnoliques diCthyle et de diphenyle et sur le triflate Cnolique. Le phosphate Cnolique diethylique donne la meilleure sterCosClectivitC. Dans les champs, les phCromones de synthitse attirent le pou de San Jose.[Traduit par la redaction]

New palladium-catalyzed approaches to heterocycles and carbocycles

“…The coordination step therefore may be crucial in formation of the 3,4-disubstituted isoquinoline, because without it the imine substrate may cyclize by either a thermal or Pd(ll)-catalyzed process to form the side product with no incorporation of the R 2 group onto the isoquinoline ring. 10 This assumption is supported by the results from the electron-rich imine 20…”

“…synthesis of isoquinolines, including the copper-catalyzed cyclization of 2-(1-alkynyl)arylaldimines to 3-substituted isoquinolines (eq 3), 10 the palladiumcatalyzed iminoannulation of internal alkynes (eq 4), 11 the electrophile-promoted cyclization of 2-(1-alkynyl)arylaldimines (eq 5) 12 and the Pd(ll)-catalyzed olefination of 2-(1 -alkynyl)arylaldimines followed by Heck reactions (eq 6). 13 This chemistry provides simple approaches to 3-monosubstituted and 3,4-disubstituted isoquinolines, which generally proceed in excellent yields.…”

“…The 3-phenylisoquinoline (2b) is believed to be formed by either the thermal or Pd(ll)-catalyzed cyclization of imine 1. 10 …”

“…Under the optimized reaction conditions above, the reactions of imine 1 with a variety of aryl iodides afforded reasonable yields of the corresponding 3,4-disubstituted isoquinolines (eq 7; Table 2, entries [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Aryl halides bearing an electron-withdrawing group in the para or meta positions usually lead to good to high yields of the 3,4-disubstituted isoquinoline products and low yields of the side product 3-phenylisoquinoline (2b) (entries 2, 4, 6, 7 and 9-11).…”

“…19 However, our attempts to prepare these two imines from their corresponding aldehydes failed. 10 Therefore, the selectivity between the mono-and disubstituted isoquinolines is determined by whether the triple bond of the 2-alkynyl imine coordinates the R 2 Pd M X intermediate A.…”