J . Am. Chem. SOC. mg, 0.48 mmol). The reaction was carried out as for lactone 4. The crude lactone was dissolved in methanol ( 2 mL). Palladium on carbon (10%) (43 mg) was added. The mixture was stirred for 44 h under hydrogen ( 1 atm), filtered through Celite, and evaporated. The residue was taken u p in dichloromethane (6 mL) and treated with an excess of diazomethane swept on a stream of argon and generated by treatment of a solution of Diazald (63 mg) in ethanol (6 mL) with a solution of potassium hydroxide (I8 mg) in water (100 rL). Flash chromatography (3 g of silica gel; SO%, 75% ether/hexane) gave the keto ester 7 as an oil (29 mg, 47%) contaminated with minor hydrogenolysis byproducts: 1991, 1 1 3, 921-939 921 'H NMR (270 MHz) 6 0.95 (m, 2 H, cyclopropyl), 1.3 (m, 2 H, cyclopropyl), 2.22 (s, 3 H, C(O)Me), 3.27 (s, 3 H, OMe), 3.84 (s, 1 H, CH2O). 5.14 (dd, 1 H, J = 8.5.4.5 Hz, PhCHN), 7.2-7.4 (m, 5 H, Ar); IR (film) 1754, 1723 cm"; MS (El) 274 (M+ -CH,CO), Abstract: Enantiomerically pure or enriched iron-carbene complexes of the type CSH5(CO)(PR,)Fe=CHCH3+ have been prepared by three routes: (a) Diastereomeric acyl complexes CSH5(CO)(PPh2R*)FeC(0)CH3 (R* = (S)-2-methylbutyl) have been prepared, separated by column chromatography, and converted by using standard techniques to (SFe,Sp)-and ( RFeSp)-CsH5(CO)( PPh2R*)Fe=CHCH,+; (b) Enantiomerically enriched (76% ee) (Rc,)-C5H5(C0)2FeCH(OCH3)CHp has been prepared from (S)-(-)-ethyl lactate and converted to enantiomerically enriched diastereomers Cp(CO)(PR,)-FeCH(OCH,)CH, (R = Me, Et). The individual diastereomers were then converted to enantiomerically enriched ethylidene complexes C5H5(CO)(PR3)Fe=CHCH3+ (R = Me, Et); (c) Racemic acyl complexes Cp(CO)(PR,)FeC(O)CH, (R = Me, Et) have been conveniently resolved via fractional crystallization of diastereomeric hydroxy carbenc salt generated by using (S)-(+)-or (R)-(-)-10-camphorsulfonic acid. The enantiomerically pure acyl complexes were converted to the corresponding enantiomerically pure carbene complexes (SFe)-and (RFe)-C5HS(CO)(PR3)Fe=CHCH3+ by using standard techniques.Enantioselective ethylidene transfer from these complexes to styrene, vinyl acetate, and isopropenyl acetate gave methylcyclopropanes in high optical yields. Ethylidene complexes C5HS(CO)(PR3)Fe=CHCH3+ (R = Me, Et), C,H,(CO)-(PPh,)Fe=CHCH3+, and CSHS(CO)(PPh2R*)Fe=CHCH3+ (R* = (S)-2-methylbutyl) were generated in the CD2C12 solution and studied by 'H and "C NMR spectroscopy. At very low temperatures (ca. -100 "C) both anticlinal (major) and synclinal (minor) isomers could be detected. Equilibrium ratios and rates of interconversion of these isomers were determined by using variable temperature 'H NMR spectroscopy. A mechanistic analysis of the transfer reaction is presented by using the stereochemical results obtained coupled with deuterium labeling and relative reactivity studies. It is concluded that the most likely mechanism for carbene transfer involves reaction of the olefin with the minor but more reactive synclinal isomer of CSHS(CO)(P...

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Highly functionalized pyrroles with appropriate regiochemical functionality represent an important class of marine natural products and potential drug candidates. We describe herein a detailed study of the reaction of α-aminoacid esters with vinylogous amides and also β-halovinylaldehydes for the regiospecific synthesis of 2,3,4-trisubstituted and 1,2,3,4-tetrasubstituted pyrroles. Since the vinylogous amides and β-halovinylaldehydes are readily available precursors, rapid access to a wide variety of unsymmetrically substituted pyrroles is accomplished via this methodology.

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