Cob(I)alamin as Catalyst. 8th Communication. Cob(I)alamin and Heptamethyl Cob(I)yrinate During the Reduction of α,β-Unsaturated Carbonyl Derivatives

Hydrogen bonds as presented in Figure 2 cannot account for the enantioselective attack of cob(I)alamin ( 4 ( I )) or heptamethyl cob(I)yrinate ( 5 ( I )) on one of the two enantiotopic faces of the substrates. The attack of the strongly nucleophilic 3d orbital is preferentially directed to the re-side of the starting materials with (Z)-configuration and leads, after the highly stereoselective reductive cleavage of the Co, C bond, to saturated products with (S)-configuration in varying enantiomeric excesses (see Schemes 1, 3 and Table 1).     

Cob (I)alamin als Katalysator 4. Mitteilung. Reduktion von α,β-ungesättigten Nitrilen

Cob(I)alamin as Catalyst. 4. Communication. Reduction of α,β-Unsaturated Nitriles Using catalytic amounts of cob (I)alamin and an excess of metallic zinc as source of electrons 1-naphthonitril ( 5 ) has been reduced to (1-naphthyl)methylamin ( 6 ) and in small amounts to (1-naphthyl)methanol ( 7 ) and (1,2,3,4-tetrahydro-1-naphthyl)methanol ( 8 ) (5 ½ h, CH₃COOH/H₂O; s. Scheme 3). Starting from cyclododecylideneacetonitrile ( 15 ) similar conditions (68 h, CH₃COOH/H₂O) produced the amines 16–19 as well as the nitrogen free saturated aldehyde 20 , the corresponding allylic alcohol 21 and the saturated derivative 22 (s. Scheme 6). It is deduced that the first attack of cob (I)alamin on an α,β-unsaturated nitrile might occur on both the nitrile dipole as well as on the carbon atom in β-position. Cob (I)alamin in aqueous acetic acid saturates the isolated double bonds in allylic alcohols and amines. In a slow reaction the two different aromatic rings of (1-naphthyl)methanol ( 7 ) have been reduced giving the corresponding tetrahydronaphthalene derivatives 8 and 12 , and in one case the production of the octahydroderivative 14 has been observed in a low yield (s. Scheme 5).     

Skeletal Migrations Observed during the Cob(I)alamin-Catalyzed Reduction of 4β-(tert-Butyl)-1β-(1-methylvinyl)cyclohexanecarbaldehyde

During the cob(I)alamin( 1(I) )-catalyzed reduction of 3 , intermediate formation of 2 and final generation of 4–10 was observed (see Scheme 1, cf. Tables 1 and 2). Identical products in similar ratios were generated starting from either 2 or 3 . Accepting the intermediate formation of six interconnected cobalt complexes, i.e. A–F (cf. Scheme 2), the generation of all the products observed can be explained.     

Cob(I)alamin als Katalysator. Retention der Konfiguration bei der reduktiv-protonenübertragenden Spaltung der Co,C-Bindung eines Alkylcobalamins. 7. Mitteilung [1]

Cob(I)alamin as Catalyst. 7. Communication [1]. Retention of Configuration during the Reductive Cleavage of the Co, C-Bond of an Alkylcobalamin Using catalytic amounts of cob(I)alamin (see Scheme 1) in aqueous acetic acid (?)-α-pinen ( 1 ) and (?)-β-pinen ( 2 ; s. Scheme 3) have been reduced. A large excess of metallic zinc served as electron source. The saturated products 5–8 (see Scheme 3) and the mechanistic aspects of their generation are discussed. The relative amounts of cis- ( 5 ) and trans-pinane ( 6 ) lead to the conclusion that the reductive cleavage of the Co, C-bond accompanied by H⁺ transfer in an alkylcobalamin occurs with retention of configuration. This result is in agreement with the corresponding cleavage of the Co,C-bond of an alkyl[hydroxy-diazaoctahydroporphinato]cobalt complex [9].     

Oxidative Fragmentations of the 5α‐ and 5β‐Hydroxy‐B‐norcholestan‐ 3β‐yl Acetates

Oxidations of 5α‐hydroxy‐B‐norcholestan‐3β‐yl acetate ( 8 ) with Pb(OAc)₄ under thermal or photolytic conditions or in the presence of iodine afforded only complex mixtures of compounds. However, the HgO/I₂ version of the hypoiodite reaction gave as the primary products the stereoisomeric (Z)‐ and (E)‐1(10)‐unsaturated 5,10‐seco B‐nor‐derivatives 10 and 11 , and the stereoisomeric (5R,10R)‐ and (5S,10S)‐acetals 14 and 15 (Scheme 4). Further reaction of these compounds under conditions of their formation afforded, in addition, the A‐nor 1,5‐cyclization products 13 and 16 (from 10 ) and 12 (from 11 ) (see also Scheme 6) and the 6‐iodo‐5,6‐secolactones 17 and 19 (from 14 and 15 , resp.) and 4‐iodo‐4,5‐secolactone 18 (from 15 ) (see also Scheme 7). Oxidations of 5β‐hydroxy‐B‐norcholestan‐3β‐yl acetate ( 9 ) with both hypoiodite‐forming reagents (Pb(OAc)₄/I₂ and HgO/I₂) proceeded similarly to the HgO/I₂ reaction of the corresponding 5α‐hydroxy analogue 8 . Photolytic Pb(OAc)₄ oxidation of 9 afforded, in addition to the (Z)‐ and (E)‐5,10‐seco 1(10)‐unsaturated ketones 10 and 11 , their isomeric 5,10‐seco 10(19)‐unsaturated ketone 22 , the acetal 5‐acetate 21 , and 5β,19‐epoxy derivative 23 (Scheme 9). Exceptionally, in the thermal Pb(OAc)₄ oxidation of 9 , the 5,10‐seco ketones 10, 11 , and 22 were not formed, the only reaction being the stereoselective formation of the 5,10‐ethers with the β‐oriented epoxy bridge, i.e. the (10R)‐enol ether 20 and (5S,10R)‐acetal 5‐acetate 21 (Scheme 8). Possible mechanistic interpretations of the above transformations are discussed.     

Cob (I)alamin als Katalysator. 3. Mitteilung [1]. Untersuchungen in Richtung einer enantioselektiven Reduktion α,β-ungesättigter Ester

Cob (I)alamin as Catalyst 3. Communication [1]. Examination of an Enantioselective Reduction Using α,β-Unsaturated Esters α,β-Unsaturated esters can be reduced to the corresponding saturated esters using catalytic amounts of cob (I)alamin in the presence of an excess of zinc. An enantioselective reduction has been observed starting from ethyl (Z)-3-methyl-5-phenyl-2-pentenoate (7).     

Nonreductive Enantioselective Ring Opening of N-(Methylsulfonyl)dicarboximides with Diisopropoxytitanium α,α,α′,α′-Tetraaryl-1,3-dioxolane-4,5-dimethanolate

The bicyclic and tricyclic meso-N-(methylsulfonyl)dicarboximides 1a–f are converted enantioselectively to isopropyl [(sulfonamido)carbonyl]-carboxylates 2a–f by diisopropoxytitanium TADDOLate (75–92% yield; see Scheme 3). The enantiomer ratios of the products are between 86:14 and 97:3, and recrystallization from CH₂Cl₂/hexane leads to enantiomerically pure sulfonamido esters 2 (Scheme 3). The enantioselectivity shows a linear relationship with the enantiomer excess of the TADDOL employed (Fig.3). Reduction of the ester and carboxamide groups (LiAlH₄) and additional reductive cleavage of the sulfonamido group (Red-Al) in the products 2 of imide-ring opening gives hydroxy-sulfonamides 3 and amino alcohols 4 , respectively (Scheme 4). The absolute configuration of the sulfonamido esters 2 is determined by chemical correlation (with 2a,b ; Scheme 6), by the X-ray analysis of the camphanate of 3e (Fig. 1), and by comparative ¹⁹F-NMR analysis of the Mosher esters of the hydroxy-sulfonamides 3 (Table 1). A general proposal for the assignment of the absolute configuration of primary alcohols and amines of Formula HXCH₂CHR¹R², X = O, NH, is suggested (see 11 in Table 1). It follows from the assignment of configuration of 2 that the Re carbonyl group of the original imide 1 is converted to an isopropyl ester group. This result is compatible with a rule previously put forward for the stereochemical course of reactions involving titanium TADDOLate activated chelating electrophiles ( 12 in Scheme 7). A tentative mechanistic model is proposed ( 13 and 14 in Scheme 7).     

Synthesis of Enantiomerically Pure D- and L-(Heteroaryl)alanines by asymmetric hydrogenation of (Z)-α-amino-αβ-didehydro esters

Homogeneous asymmetric hydrogenation of a wide range of methyl and tert-butyl (Z)-2-(acylamino)-3-(heteroaryl)acrylates (see 1a–f and 2a–d, f, g , resp.) catalyzed by diphosphinerhodium catalysts was studied for the synthesis of enantiomerically pure 3-furyl-, 3-thienyl-, and 3-pyrrolylalanines (see 3a–f , and 4a–d, g ; Scheme 1). The precursors, the (Z)-α-amino-α,β-didehydro esters 1a–f and 2a–d, f, g were prepared in high yields using the phosphorylglycine-ester method (Scheme 1). Isomerically pure (Z)-α-amino-α,β-didehydro esters were required to obtain the highest enantiomeric excesses (ee's) in the asymmetric hydrogenation, and the tert-butyl-ester strategy was beneficial in terms of both getting pure (Z)-α-amino-α,β-didehydro esters and obtaining high ee's in the hydrogenation. Finally, in contrast to the methyl-ester series, deprotection of the tert-butyl esters 4a–d, g was easily performed using CF₃CO₂H without any racemization.     

Cob(I)alamin als Katalysator. 6. Mitteilung [1]. Bildung und Fragmentierung von Alkylcobalaminen,ein Gleichgewichtsprozess zwischen nukleophiler Addition und reduktiver Fragmentierung

Cob(I)alamin as Catalyst. 6. Communication [1]. Formation and Fragmentation of Alkylcobalamins: the Nucleophilic Addition – Reductive Fragmentation Equilibrium Isolated olefines can be saturated using catalytic amounts of cob(I)alamin in aqueous acetic acid; as electron source an excess of zinc dust is added to the solution containing the homogeneous catalyst. During this overall hydrogenation of isolated double bonds intermediate alkylcobalamins are formed (compare e.g. Schemes 2, 4, 5, 7 and 12). Clear evidence is presented that the nucleophilic attack on the isolated double bond is carried out by cob(I)alamin and not by cob(II)alamin also present in the system (see Scheme 3b and 3c). As this catalytic saturation of olefins depends on the pH of the solution, characterized by a slow reaction at pH = 7.0 compared to the same reduction in aqueous acetic acid (see Scheme 2, 2 → 4 , and Scheme 3a), it is reasonable to accept the participation of an electrophilic attack by a proton during the generation of alkylcobalamins. – We use the term nucleophilic addition to describe the formation of alkylcobalamins from a proton, an olefin and cob(I)alamin (compare Schemes 4–7 and 12). A special sequence of experiments showed the nucleophilic addition to be regioselective. Preferentially the higher substituted alkylcobalamin revealed to be produced. Therefore, the nucleophilic addition of cob(I)alamin follows the Markownikoff rule (compare chap. 4: formation and fragmentation of β-hydroxyalkylcobalamins). Under the reaction conditions applied the intermediate alkylcobalamins can be present in base-on and base-off forms. They are known to exist as octahedral complexes and might also be stable to some extent as tetragonal-pyramidal species. In addition the base-off forms can partially be protonated at the dimethylbenzimidazole moiety in aqueous acetic acid (compare Scheme 12). From this equilibrium of intermediate alkylcobalamins three modes of decay disclosed to be possible: (i) The reductive fragmentation leading to an olefin, a proton, and cob(I)alamin is the formal retro-reaction of the nucleophilic addition (see Schemes 2, 4 and 6–12). This equilibrium of an associated alkylcobalamin and the corresponding dissociation products revealed to be a fast process compared to the reductive cleavage of the Co, C-bond cited below (s. (iii)). (ii) As the second reaction pattern an oxidative fragmentation producing an olefin, a hydroxy anion (or water, respectively) and cob (III)alamin has been observed (see Schemes 7, 8, 10 and 12). (iii) The slow reductive cleavage of the Co, C-bond, initiated by addition of electrons (see [1a] [24]), was the third reaction path observed (see Schemes 2, 4–8 and 10–12). – The stereochemistry of the three transformations originating from the intermediate alkylcobalamins is unknown up to now. The antiperiplanar pattern of the fragmentation reactions presented in the Schemes has been chosen arbitrarily (see e.g. Scheme 12).     

Cob(I)alamin-Catalyzed Skeletal Migrations Observed during the Reduction of 4β-(tert-Butyl)-1α-(1-methylvinyl)cyclohexanecarbaldehyde

The cob(I) alamin (1(I)) -catalyzed² transformation of the aldehyde 2 has been studied (cf. Table 1). Kinetic examinations showed a rapid isomerization of 2 to 3 (cf. Fig. 1 and 2). From the transformations in glacial AcOH, the two cyclopropanols 5 and 7 were isolated as main products (cf. Tables 1–3 and Fig. 1 and 2). Using large amounts of 1(I) , the aldehyde 4 was very slowly transformed. Accepting the intermediate formation of 6 interconnected Co-complexes, i. e. A , B , C , D , E and F (cf. Scheme), the generation of all the products observed can be explained.     

The First Fully Planar C5‐Conformation of Homooligopeptides Prepared from a Chiral α‐Ethylated α,α‐Disubstituted Amino Acid: (S)‐Butylethylglycine (=(2S)‐2‐Amino‐2‐ethylhexanoic Acid)

An optically active α‐ethylated α,α‐disubstituted amino acid, (S)‐butylethylglycine (=(2S)‐2‐amino‐2‐ethylhexanoic acid; (S)‐Beg; (S)‐ 2 ), was prepared starting from butyl ethyl ketone ( 1 ) by the Strecker method and enzymatic kinetic resolution of the racemic amino acid. Homooligopeptides containing (S)‐Beg (up to hexapeptide) were synthesized by conventional solution methods. An ethyl ester was used for the protection at the C‐terminus, and a trifluoroacetyl group was used for the N‐terminus of the peptides. The structures of tri‐ and tetrapeptides 5 and 6 in the solid state were solved by X‐ray crystallographic analysis, and were shown to have a bent planar C₅‐conformation (tripeptide) and a fully planar C₅‐conformation (tetrapeptide) (see Figs. 1 and 2, resp.). The IR and ¹H‐NMR spectra of hexapeptide 8 revealed that the dominant conformation in CDCl₃ solution was also a fully planar C₅‐conformation. These results show for the first time that the preferred conformation of homopeptides containing a chiral α‐ethylated α,α‐disubstituted amino acid is a planar C₅‐conformation.     

Photochemische Reaktionen 111. Mitteilung [1] Zur Photochemie α, β-ungesättigter γ, δ-Epoxyester I: Singulett- versus Triplettreaktivität

On triplet excitation (E)- 2 isomerizes to (Z)- 2 and reacts by cleavage of the C(γ), O-bond to isomeric δ-ketoester compounds ( 3 and 4 ) and 2,5-dihydrofuran compounds ( 5 and 19 , s. Scheme 1). - On singulet excitation (E)- 2 gives mainly isomers formed by cleavage of the C(γ), C(δ)-bond ( 6–14 , s. Scheme 1). However, the products 3–5 of the triplet induced cleavage of the C(γ), O-bond are obtained in small amounts, too. The conversion of (E)- 2 to an intermediate ketonium-ylide b (s. Scheme 5) is proven by the isolation of its cyclization product 13 and of the acetals 16 and 17 , the products of solvent addition to b . - Excitation (λ = 254 nm) of the enol ether (E/Z)- 6 yields the isomeric α, β-unsaturated ε-ketoesters (E/Z)- 8 and 9 , which undergo photodeconjugation to give the isomeric γ, δ-unsaturated ε-ketoesters (E/Z)- 10 . - On treatment with BF₃O(C₂H₅)₂ (E)- 2 isomerizes by cleavage of the C(δ), O-bond to the γ-ketoester (E)- 20 (s. Scheme 2). Conversion of (Z)- 2 with FeCl₃ gives the isomeric furan compound 21 exclusively.     

Steroid Total Synthesis,Part II; (−)-17β-Hydroxy-des-A-androst-9-en-5-one

Based on the results obtained in the racemic series (part I), (—)-17β-hydroxy-des-A-androst-9-en-5-one has been synthesized, starting with (S)-(—)-5-heptanolide. The key step, viz. the condensation of (S)-(—)-7-hydroxy-1-nonen-3-one (or its amine adduct) with 2-methyl-cyclopentane-1, 3-dione involves an asymmetric induction. Model experiments with (R)-(+)-5-decanolide leading to the enantiomeric homolog of the BCD-tricyclic compound are also described.     

Efficient Synthesis of (−)‐(R)‐Muscone by Enantioselective Protonation

A new synthesis of (?)‐(R)‐muscone ((R)‐ 1 ) by means of enantioselective protonation of a bicyclic ketone enolate as the key step (see 6 →(S)‐ 4 in Scheme 2) is presented. The C₁₅ macrocyclic system is obtained by ozonolysis (Scheme 7).     

Kupplung von Peptiden mit C-terminalen α,α-disubstituierten α - Aminosäuren via Oxazol-5(4H)-one

Peptide-Bond Formation with C-Terminal α,α-Disubstituted α - Amino Acids via Intermediate Oxazol-5(4H)-ones The formation of peptide bonds between dipeptides 4 containing a C-terminalα,α-disubstituted α-amino acid and ethyl p-aminobenzoate ( 5 ) using DCC as coupling reagent proceeds via 4,4-disubstituted oxazol-5(4H)-ones 7 as intermediates (Scheme 3). The reaction yielding tripeptides 6 (Table 2) is catalyzed efficiently by camphor-10-sulfonic acid (Table 1). The main problem of this coupling reaction is the epimerization of the nonterminal amino acid in 4 via a mechanism shown in Scheme 1. CSA catalysis at 0° suppresses completely this troublesome side reaction. For the coupling of Z-Val-Aib-OH ( 11 ) and Fmoc-Pro-Aib-OH ( 14 ) with H-Gly-OBu¹ ( 12 ) and H-Ala-Aib-NMe₂ ( 15 ), respectively, the best results have been obtained using DCC in the presence of ZnCl₂ (Table 3).     

Preparation and Structures of 2‐Substituted 5‐Benzyl‐3‐methylimidazolidin‐4‐one‐Derived Iminium Salts,Reactive Intermediates in Organocatalytic Transformations Involving α,β‐Unsaturated Aldehydes

Preparations of the title compounds, 5 – 7 (Scheme 1 and Table 1), of their ammonium salts, 9 – 11 (Scheme 2 and Table 2), and of the corresponding cinnamaldehyde‐derived iminium salts 12 – 14 (Scheme 3 and Table 3) are reported. The X‐ray crystal structures of 15 cinnamyliminium PF₆ salts have been determined (Table 4). Selected ¹H‐NMR data (Table 5) of the ammonium and iminium salts are discussed, and structures in solution are compared with those in the solid state.     

Über die Stereoselektivität der α-Alkylierung von (1R, 2S) (+)-cis-2-hydroxy-cyclohexancarbonsäureäthylester

The Stereoselectivity of the α-Alkylation of (+)-(1R, 2S)-cis-Ethyl-2-hydroxy-cyclohexanecarboxylate In continuation of our work on the stereoselectivity of the α-alkylation of β-hydroxyesters [1] [2], we studied this reaction with the title compound (+)- 2 . The latter was prepared through reduction of 1 with baker's yeast. Alkylation of the dianion of (+)- 2 furnished (?)- 4 in 72% chemical yield (Scheme 1) and with a stereoselectivity of 95%. Analogously, (?)- 7 was prepared with similar yields. Oxidation of (?)- 4 and (?)- 7 respectively furnished the ketones (?)- 6 (Scheme 3) and (?)- 8 (Scheme 4) respectively, each with about 76% enantiomeric excess (NMR.). It is noteworthy that yeast reduction of rac- 6 (Scheme 3) is completely enantioselective with respect to substrate and product and gives optically pure (?)- 4 in 10% yield, which was converted into optically pure (?)- 6 (Scheme 3). The alkylation of the dianionic intermediate shows a higher stereoselectivity (95%) from the pseudoequatorial side than that of 1-acetyl- or 1-cyano-4-t-butyl-cyclohexane (71% and 85%) [9] or that of ethyl 2-methyl-cyclohexanecarboxylate (82%). The stereochemical outcome of the above alkylation is comparable with that found in open chain examples [1] [2]. Finally (+)-(1R, 2S)- 2 was also alkylated with Wichterle's reagent to give (?)-(1S, 2S)- 9 in 64% yield. The latter was transformed into (?)-(S)- 10 and further into (?)-(S)- 11 (Scheme 5). (?)-(S)- 10 and (?)-(S)- 11 showed an e.e. of 76–78% (see also [11]). Comparison of these results with those in [11] confirmed our former stereochemical assignment concerning the alkylation step.     

Preparation and Transmetallation of a Triphenylstannyl β-D-Glucopyranoside: A highly stereoselective route to β-D-C-glycosides via glycosyl dianions

The triphenylstannyl β-D -glucopyranoside 4 was synthesized in one step from the 1,2-anhydro-α-D -glucopyranose 3 with (triphenylstannyl)lithium (Scheme 1). Transmetallation of 4 with excess BuLi, followed by quenching the dianion 7 with CD₃OD gave (1S)-1,5-anhydro-3,4,6-tri-O-benzyl-[1-²H]-D - glucitol ( 8 ) in 81% yield (Scheme 2). Trapping of 7 with benzaldehyde, isobutyraldehyde, or acroleine gave the expected β-D -configurated products 11, 12 , and 13 in good yields. Preparation of C-acyl glycosides from acid chlorides, such as acetyl or benzoyl chloride was not practicable, but addition of benzonitrile to 7 yielded 84% of the benzoylated product 14 . Treatment of 7 with MeI led to 15 (30%) along with 40% of 18 , C-alkylation being accompanied by halogen-metal exchange. Prior addition of lithium 2-thienylcyanocuprate increased the yield of 15 to 50% and using dimethyl sulfate instead of MeI led to 77% of 15 . No α-D -anomers could be detected, except with allyl bromide as the electrophile, which yielded in a 1:1 mixture of the anomers 16 and 17 .     

Nucleophilic additions to N-glycosylnitrones part IV Asymmetric synthesis of N-hydroxy-α-aminophosphonic and α-aminophosphonic acids

The addition of phosphite anions and of tris(trimethylsilyl) phosphite (P(OSiMe₃)₃) to N-glycosyl-C-arylnitrones was examined. While these nitrones proved inert towards the phosphite anions, they reacted with P(OSiMe₃)₃ under catalysis by Lewis acids. Thus, P(OSiMe₃)₃ reacted with the crystalline (Z)-N-glycosylnitrones 2 and 8 to give the optically active N-hydroxy-α-aminophosphonic acids 4 and 10 , respectively, and hence the α-aminophosphonic acids 5 and 11 in yields up to 92% and with an enantiomeric excess (e.e.) up to 97% (Scheme 1). The absolute configuration of the phosphonates depend upon the nature and – in one case – upon the quantity of the catalyst (Figure). Upon catalysis by HCIO₄ or Zn(OTF)₂, p(OSiMe₃)₃ added to 2 to give, in both cases, the (+)-(R)-phenylphosphaglycine 5 (optical purity 79–84 and 90–93%, resp.). The optical purity (o.p.) was hardly influenced by the amount of these catalysts (0.02-;1 equiv.). However, catalysis by ZnCl₂ gave, with trace quantities of the catalyst, (–)-(S)- 5 (o.p. 79%), while an equimolar amount of ZnCl₂ yielded (+)-(R)- 5 (o.p. 82%). The HClO₄-catalyzed addition of P(OSiMe₃)₃ to the nitrone 14 (Scheme 2) led to (+)-(R)-N-hydroxyphosphavaline 15 (78%) and hence to (–)-(R)-phosphavaline 16 (71% from 14 e.e. 95%). Under conditions leading from the nitrones 2 , 8 , 14 , and 20 (Schemes 1 and 2) predominantly to (R)-α-aminophosphonic acids, the addition of P(OSiMe₃)₃ to nitrone 18 , possessing a benzyloxy substituent as an additional potential ligand for the catalyst, gave (S)-phosphaserine 19 . The addition of P(OSiMe₃)₃ to the nitrone 20 , catalyzed by Zn(OTf)₂, led to (+)-(R)-N-hydroxyphosphamehionine 21 (71%, e.e. 77%) and hence to (–)-(R)-phosphamethionine 22 (77% from 20 , e.e. 79%). Catalysis by trace quantities of ZnCl₂ gave (+)-(S)- 22 (85%, e.e. 61%). The enantiomerically pure aminophosphonic acids 5 , 11 , and 16 were obtained by recrystalliztion. The e.e. of the N-hydroxyaminosphosphonic acids 10 , 15 , and 21 and the aminophosphonic acids 5 , 11 , 16 , and 22 were determined by the HPLC analysis of the dimethyl N-naphthoyl-α-aminophosphonats 7 , 13 , 17 , and 23 , on a chiral stationary phase.     

α-Methylidene- and α-Alkylidene-β-lactams from Nonproteinogenic Amino Acids

Treatment of methyl 2-(1-hydroxyalkyl)prop-2-enoates 1 with conc. HBr solution afforded methyl (Z)-2-(bromomethyl)alk-2-enoates 2 , which were transformed regioselectively into N-substituted methyl (E)-2- (aminomethyl)alk-2-enoates 3 (S_N2 reaction) and into N-substituted methyl 2-(1-aminoalkyl)prop-2-enoates 4 (S_N2′ reaction). Regiocontrol of nucleophilic attack by amine was accomplished simply by choice of solvent, the S_N2 reaction occurring in MeCN and the S_N2′ reaction in petroleum ether. Hydrolysis and lactamization afforded β-lactams 7 and 8 , containing an exocyciic alkylidene and methylidene group at C(3), respectively.