Acyl-oxygen cleavage in the alkaline hydrolysis of activated vinyl esters

Abstract

carried out are summarized in Table I.It should be noted that under these reaction conditions allylic C-H insertion, to produce 9, competes effectively with the usually efficient7® intramolecular cyclopropanation.8 Methylene C-H insertion is substantially more rapid than methyl C-H insertion,9 allowing clean formation of 10. While it might be extrapolated that methine should be more efficient than methylene insertion, ring-size effects predominate, so that 7 is formed from 2.The functionalized cyclopentanes produced by this cyclization should be versatile intermediates for elaboration to complex natural products. Keto ester 10, for example, prepared by Tsuji,10 has been converted by him to methyl dihydrojasmonate10 and 18-hydroxyestrone.11 Experimental Section General Methods. XH NMR spectra were determined on a JEOLCO MH-100 spectrometer as solutions in CDC13. Chemical shifts are reported in parts per million downfield from the internal reference tetramethylsilane. Couplings (J) are in hertz. The infrared spectra (IR) were recorded on a Perkin-Elmer 257 spectrometer as solutions in CC14 and are reported in reciprocal centimeters. Mass spectra were determined at 70 eV on an LKB 9000 gas chromatograph-mass spectrometer interfaced with a PDP-12 computer system and are reported as mass per unit charge, with intensities as a percentage of the peak of greatest ion current having m/z> 100 in parentheses. High-resolution mass spectroscopy was carried out on a VG 7070f double-focusing mass spectrometer. Organic chemicals were purchased from Aldrich Chemical Co. Organometallics were purchased from Alfa Inorganics and were titrated prior to use. Solvent mixtures (e.g., 5% ethyl acetate/hexane) are volume/volume mixtures. The Rf values indicated refer to thin-layer chromatography on Analtech 2.5 X 10 cm, 250-fim analytical plates coated with silica gel GF.Column chromatography was carried out by using TLC-mesh silica gel, following the procedure we have described.12 Preparation of 6.13 Diazo ester 1 (1.55 g, 5.50 mmol), prepared by alkylation of the dianion of methyl acetoacetate1 234 5followed by diazo transfer,5,6 was diluted with 30 mL of CH2C12 (dried by filtration through K2C03) under N2. Rhodium(II) acetate7 (0.040 g) was added, and the mixture stirred at room temperature for 30 min. Vigorous gas evolution was observed, and the solution turned a bright emerald green. The reaction mixture was diluted with 4% aqueous HC1 and extracted with CH2C12. The combined organic extracts were dried over Na2S04 and concentrated in vacuo.

Triflate/Mesylate Ratios and Competing C−O and S−O Bond Cleavages in Nucleophilic Vinylic Substitution

“…We know of only two cases where attack on a multiatom ester nucleofuge predominated completely over the competing reaction at the vinylic carbon. 16 The nucleophile was OH -/H 2 O. In the analogous reaction with p-MeC 6 H 4 Sthe products indicated a ca.…”

“…All of these examples are for competition of reactions of nucleophilic olefins. We know of only two cases where attack on a multiatom ester nucleofuge predominated completely over the competing reaction at the vinylic carbon . The nucleophile was OH - /H 2 O.…”

“…In the analogous reaction with p -MeC 6 H 4 S - the products indicated a ca. 1:1 competition between reaction on the vinylic carbon and the carbonyl …”

“…S-O bond cleavage in nucleophilic reactions of vinyl sulfonates were previously observed for nucleophilic vinyl sulfonates. 13 Whereas most cycloalkenyl triflates solvolyze via S N 1, 4b cyclopentenyl triflate gives [ 16 O]cyclopentanone in 50% ethanol-H 2 18 O, excluding an S N 1 route and suggesting reaction via an S-O bond cleavage. 13b Other cyclic triflates with geometrical constraints react similarly.…”

“…1:1 competition between reaction on the vinylic carbon and the carbonyl. 16 Consequently, the reactions demonstrated by eqs 8, 10, 11, and 13 add one more variant to the multitude of reactions routes leading to or competing with vinylic substitution. 17 Whereas triflates should be more prone than mesylates to react via a concerted route (eq 2) the possibility that the different behavior of triflates and mesylates is due to the intervention of this route for the triflates is unlikely with our moderately activated system based on what is known for nucleophilic vinylic substitutions.…”