Dedicated to Professor Dr. Ulrich Schiillkopf on the occasion of his 60th birthday (30.VII. 87) Racemic and enantiomerically pure methyl N-(tert-butyl)-N-benzyl-and N-I-(phenylethy1)aziridinecarhoxylates are prepared by known methods and converted to phenyl thioesters (1,2, 15, 16; Schemes 2 and 3 ) . These are deprotonated with lithium diisopropylamide (LDA) and BuLi (for removal of diisopropylamine) in THF at dry-ice temperature. The resulting lithiated species are surprizingly stable ;and are deuterated, alkylated (CH,, C2H,, allyl, benzyl), and added to aldehydes and nitroolefins in good yields (5MO %, 18 examples; Schemes 1 and 4 4 ) . The configurational stability of the lithiated species is studied, and conclusions about their structures are drawn. Thus, a C(a)-lithiated ester (see L, Scheme 9 ) or an 0-lithiated 'enolate' (see M) with pyramidalized C@)-atom is proposed for the species from levorotatory S-phenyl N-benzylaziridinecarbothioate which does not undergo racemization after 1 h at -60" (THF solution). Scheme2 1) PhCHO. NaBH, COOMe 2) MeOH. HCI c PicH,HN + H HCi CH,OH 11 CH,OH ( 45% ) j ( 13% ) 1 PPh3, CBr,, NEt, ( 35% ) 1678HBLVETICA CHIMICA ACTA ~ Val. 70 (1987) compound follows from the high-field 'H-NMR spectrum (NOE measurements and unchanged spectra from -100 to +loo"). The overall yield of the four-step sequence was 13%, not enough to render (-)-2 a useful starting material for syntheses'). A more convenient access to aziridine esters of either chirality sense at the stereogenic ring C-atom was pointed out to us by J. P . Obrecht4): the two diastereoisomers 13 and 14 obtained as a 1 : 1 mixture [7] in 85 % yield from (S)-( 1-phenylethy1)amine and rac-2,3-dibromopropionate (both commercial) were separated by flash chromatography (40-g scale on 1 kg of silica gel) and almost quantitatively converted to the crystalline thioester 15 and its oily diastereoisomer 16. The configuration of the methyl esters 13 and 14 was determined by acidic ring opening (HClO,/H,O) and hydrogenolysis (Pd(OH),/C) to ( S )and (R)-serine, respectively, establishing the configurations of all four aziridines shown in Scheme 3. Schrrne 3 Ph NEt, MeANHp + BrJCOOMe -----+ COOMe Toluene 13 (-(S)-Serine) 14 ( + (R)-Serine) (chrom. separation) 15 (cryst.) 16 (oil) 3. Deprotonation, Deuterolysis, and Methylation of the trans-(2s)-Aziridine Thioester (-)-2 with Retention of Configuration. -Treatment of the thioester (-)-2 with base5) and CD,OD or CH,I/DMPU6) as shown in Scheme 4 gave, after isolation, still optically active products 17 and (-)-8, respectively. 3, 4, ' ) N-Tritylserine ester can also becyclized [6a]. We plan to apply the N-unprotected aziridine ester thus available in future investigations with substituents on the N-atom [6b] different from those used here. We thank Dr. J. P . Obrecht (Socar AG, Diibendorf, Switzerland) for a private communication about the ease with which diastereoisomers such as 13 and 14 can be chromatographically separated. For complete D-incorporation, it was necessary to first add LDA,...

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The [32] cycloaddition of alkenyl Fischer carbene complexes 1 and 6 with diazomethane derivatives to give D 2 -pyrazoline carbenes 2, 4, and 7 is described. The conversion of (À)-8-phenylmenthol-derived carbenes 6 into pyrazoline esters 9 through a one-pot cycloaddition ± protection ± oxidation is presented as an expeditious route to enantiomerically pure 3-alkoxycarbonyl-D 2 -pyrazolines in good yields and in a highly regio-and diastereoselective manner. Pyrazolidines 13 were synthesized in excellent overall yields from 9 through pyrazolines 11 and 12, the diastereoselective reduction of CN bond being the key step. Azaprolines 16 and 17 were prepared in very good yields from epimeric trans-13 or cis-13 by oxidative deprotection of the silylated hydroxy group. In an alternative reaction, the pyrazolidine ring of 13 was reduced to obtain protected openchain 2,4-diamino alcohols 19 with three chiral centers.

A new procedure for the synthesis of 1,3,4-trisubstituted and 1,4-disubstituted pyrrolidin-2-one derivatives in an enantioselective fashion is reported. The 1,3-dipolar cycloaddition of (+/-)-menthol and (-)-8-phenylmenthol derived Fischer alkoxy alkenyl carbene complexes with in situ generated functionalized azomethine ylides gives the corresponding cycloadducts as chelated tetracarbonyl Fischer carbene complexes. Only one regioisomer is detected in all cases, and the diastereoselectivity of the reaction is very high when (-)-8-phenylmenthol derived carbenes are employed. Oxidation and further transformation of the cycloadducts provide an easy access to pyrrolidin-2-ones. The anti-inflammatory and antidepressant drug (+)-Rolipram is readily prepared in four steps in a 20% overall yield by taking advantage of this newly developed methodology.

The reaction of tert‐butylalkynyl chromium Fischer carbene complex 1 with nitrones 2 affords β‐enamino‐ketoaldehydes 4 by the light‐promoted rearrangement of the corresponding [3+2] cycloadduct carbene complexes 3. On the other hand, [3+2] cycloaddition of chiral nonracemic Fischer alkenyl carbene complexes 19 with nitrilimines 10 yields enantiomerically pure Δ2‐pyrazolines with high regio‐ and diastereoselectivity.