Lactonization/benzylic triflation

Intramolecular cyclopropanations are also well documented in the literature. It has been shown by Koskinen and co-workers that the cyclopropanation of diazomalonate 57, illustrated in Figure 9.18, using benzyl bis(oxazoline) 40 and copper(I) triflate afforded lactone 58 in 73% yield and 32% ee. Nishiyama and coworkers showed that cyclopropanations of diazoacetates 59a-c proceeded in yields ranging from 79-93% and 24-86% ee (Table 9.6, Fig. 9.18, p. 544). ... 

Analogues of 70 have been prepared by various methods including nucleophilic displacement of triflate esters attached directly to the oxetane ring (see Section 2.05.7.2) <2001TL4247>, from xylose, 145, via the benzyl-idene-protected oxetane, 146 (Scheme 24) <2004TA2667>, or from L-rhamnose, 147, via a l,4-lactone-2-O-triflate, 148 (and key oxetane 149 (Scheme 25)) <2004TA2681>. The /3-azidoester monomers formed by these methods were converted to the /3-amino acids and subsequently to /3-peptides by reduction of the azide and ester hydrolysis. 

Synthesis from D-glucuronolactone Synthesis of bulgecinine from D-glucuro-nolactone derivative 27 has been reported (Scheme 4). Triflation of the lactone 27 followed by nucleophilic displacement of the triflate group with azide ion and then hydrogenation and protection with benzyl chloroformate produced 28. Conversion of 28 to the unstable aldehyde 29 followed by reduction in situ by sodium borohydride afforded the crystalline diol 30, with no epimerization at C-5. Selective mesylation of 30 gave the mesylate... 

A mixture of phenylacetic acid, benzyl alcohol, and tri-n-butylamine in methylene chloride added under argon to a mixture of l-methyl-2-bromopyridinium iodide and methylene chloride, and refluxed 3 hrs. benzyl phenylacetate. Y 97%. F. e., also with l-methyl-2-chloropyridinium iodide, s. T. Mukaiyama et al., Chem. Lett. 1975, 1045 Bull. Chem. Soc. Japan 50, 1863 (1977) carboxylic acid amides from amines (cf. Synth. Meth. 26, 367) s. ibid. 1975, 1163 3,4-dihydro-2H-pyrido-[1,2-a]pyrimid-2-one as acid scavenger cf. ibid. 1976, 13, 57 lactones from hydroxycarboxylic acids (cf. Synth. Meth. 17, 320) with 2-chloropyridine methio-dide and triethylamine s. ibid. 1976, 49 esters with 2 halogeno-3-ethylbenzothia-zolium salts of ibid. 1976, 267 2-chloro-N-methylbenzothiazolium triflate as condensing agent s. F. Souto-Bachiller, G. S. Bates, and S. Masamune, Chem. Com-mun. 1976, 719. 

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