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The Diels-Alder reaction of chiral 2-alkylsulfinyl-1-nitroalkene 1 and Danishefsky's diene (2) afforded adducts 3 and 4 in good chemical yield with a high enantiomeric excess, while diastereomeric nitroalkene 7 gave 8 and 9 , enantiomeric to 3 and 4 , respectively

The previously proposed structure of an acid-induced dehydration product of physalin A, a 13,14-seco-16,24-cyclosteroid, is revised as having a new carbon skeletal structure named neophysalin. The reaction from physalins to neophysalins proceed via a kind of the benzilic acid rearrangement.

Using the high pressure technique, asymmetric Diels-Alder reaction utilizing chiral 2-nitro-1-sulfinylolefins and dienes proceeded smoothly to give highly functionalized cyclohexene derivatives with satisfactory chemical yield and high diastereomeric excess.

The asymmetric total synthesis of thienamycin-like γ-lactam 1 and its analogue 2 has been accomplished by utilising highly diastereoselective alkylation of tin(II) enolate 5 on acyl imine obtained in situ from chiral 3-substituted 5-acetoxypyrrolidin-2-one 3.

New 5-deazaflavinocyclophane with planar chirality, a novel flavoenzyme model, has been synthesized. This compound provides the first example for selective diastereoface-differentiation during its own reduction and oxidation.

The reactions of protected serine- and threonine-derived γ-(mesyloxy) α,β-unsaturated esters with various magnesio organocyanocopper Lewis acid complexes have been investigated. The formation of syn-S N 2' products in addition to the normally expected anti-S N 2'products is taken as an indication that the reaction proceeds by a mechanism involving coordination of the magnesiocuprate with the C(δ)-N:C(γ)-O syn-γ-(mesyloxy) α,β-enoates

A chiral phosphonoacetate 2 differentiates the enantiotopic carbonyl groups in an α-diketone 5 to afford the Z-olefin 6 in high yield and ee. The absolute stereochemistry of 6 was determined by X-ray analysis of 8 derived from 6.

The stereoselective synthesis of biologically important vinylglycine derivatives by reaction of homochiral 4-methoxycarbonyl-5-vinyloxazolidin-2-ones with organocopper reagents is described; 4,5-trans-oxazolidin-2-one 6 yields (E)-vinylglycines as the major products by treatment with the ‘higher order’ cyanocuprate–BF3 reagents or trialkylzincates in the presence of cuprous cyanide, 4,5-cis-oxazolidin-2-one 10 affords only the desired (E)-vinylglycines.

Several chiral 2-nitro-1-sulfinylalkenes were prepared and examined for their utility as dienophiles for asymmetric [4+2] cycloaddition. Trisu- bstituted dienophiles (3-6) undergo distereoselective cycloaddition with cyclopentadiene in the presence of Lewis acids. Even the tetrasubsti- tuted chiral sulfinyl dienophiles (1) and (2) could be coerced into un- dergoing [4+2] cycloaddition to afford the cycloadducts in high yield without concomitant elimination if the reaction was conducted under high pressure. Generally, the Z-sulfinyl dienophiles (1-4) showed higher diastereo- and exdo/exo-selectivity than the E-dienophiles (5) and (6)

Regio- and stereo-selective synthesis of (E)-alkene dipeptide isosteres has been successfully achieved by exposing both (E)- and (Z)-N-(4-methylphenyl)sulfonyl-γ,δ-epimino-α,β-enoates to organocopper reagents at –78 °C for 30 min.

The stereospecific synthesis is described of the first member of a new class of C-nucleoside analogues in which the sugar ring is replaced with a 1, 3-thiazolidine ring. The 1, 3-thiazolidin-2-yl analogues (1) and (2) of pseudouridine were prepared stereospecifically via condensation of L or D-cysteine with a formylated nucleobase.

Enantiomerically pure (1 R ,2 R ,4 R ,5 R )- and (1 S ,2 R ,4 S ,5 R )-2,5-diphenyl-1,4-diazabicyclo[2.2.2]octane (2,5-diphenyl-DABCO) have been prepared and their crystal structures studied.

Azamacrocycles 1–4 were synthesized from 9 in 20–30% overall yields. Compounds 1 and 2 extracted some metal ions into organic solvents, but 3 and 4 did not. The crystal structure of the Ag(I) complex of 1 has been determined.

The enantiomers, (R)-(-)-1 and (S)-(+)-1, of (+/-)-4-amino-N-[2-(1-azabicyclo[3.3.0]octan-5-yl)ethyl]-5-chloro-2,3- dihydro-2-methylbenzo[b]furan-7-carboxamide [(+/-)-1] were prepared from optically active benzyl 4-acetylamino-2,3-dihydro-2-methylbenzo[b]furan-7-carboxylate [(R)-(+)-6, (S)-(-)-6], respectively. The requisite (R)-(+)-6 and (S)-(-)-6 were prepared by large-scale preparative HPLC on chiral stationary phases (CSPs). The absolute configuration of (S)-(+)-1 was determined by single crystal X-ray analysis. The serotonin 5-HT4 receptor agonistic activity of (S)-(-)-1 hemifumarate (SK-951) which was hemifumarate of (S)-(+)-1 was about twice that of the other enantiomer (R)-(+)-1 hemifumarate which was hemifumarate of (R)-(-)-1.

Amino allenes have been synthesized from 2-ethynylaziridines via organocopper-mediated reactions. Whereas treatment of enantiomerically pure (2 R,3 S)-2,3-trans-3-alkyl-2-ethynylaziridines with RCu(CN)M (M = Li or MgX) yield exclusively (S,S)-allenylamines in high yields, isomeric (2 S,3S)-2,3-cis-3-alkyl-2-ethynylaziridines afford (S,R)-allenylamines in comparable high yields.

Whereas treatment of the allylic mesylates of N -protected 2-alkyl-4-amino-( E )-2-alken-1-ols with sodium hydride in DMF yields exclusively the corresponding 2,3- trans -2-alkenyl-3-alkylaziridines, exposure of the methyl carbonates of N -protected 2-alkyl-4-amino-( E )-2-alken-1-ols to Pd(PPh 3 ) 4 (5–20 mol%) in THF or 1,4-dioxane affords predominantly the corresponding 2,3- cis -2-alkenyl-3-alkylaziridines. These reactions can be used to synthesize either of two diastereomers from single common intermediates.

Seven novel cycloartane-type triterpenes were isolated from Combretum quadrangulare , and their structures were elucidated on the basis of spectral analysis. All these compounds were tested for their cytotoxicity against murine colon 26-L5 carcinoma cells. Methyl quadrangularate B ( 2 ) and methyl quadrangularate D ( 4 ) exhibited potent cytotoxicity having ED 50 values 9.54 and 5.42 μM, respectively.

Treatment of 8, 8-dibromobicyclo [5.1.0] octanes (A) with a higher order organocuprate prepared from cuprous thiocyanate (method A) or cuprous cyanide (method B) and methyllithium, followed by the addition of methyl iodide in situ, readily afforded 8, 8-dimethylbicyclo [5.1.0] octanes (B) in good yields. The results are summarized in Table I. Interestingly, reaction of the cisdibromides (4 and 19) under the present conditions gave tricyclic compounds (15 and 16, and 20, respectively)

Etude de la synthese d'alcoxy-6 methylseleno-5 penamecarboxylates-3 d'alkyle (A) par cycloaddition d'alcoxycetenes et de methylseleno-2 thiazoline-2carboxylates-4 d'alkyle; demethylselenation de A par reduction selective

Reaction of (E)-ethyl 3β-t-butyldimethylsiloxypregna-5,17-dien-21-oate with lithium di-isopropylamide followed by alkyl halides results in the predominant formation of (20S)-alkylation products in >88% isolated yields; a synthetic application to both (20R)- and (20S)-steroidal side chains is also described.

A highly diastereocontrolled alkylation at the C-4 position of 4-acetoxyazetidin-2-one (5) employing chiral tin(II) enolates of heteroatom-substituted acetyl derivatives (3a–e) furnishes new synthetic intermediates (6a–e) for 1β-heteroatom-substituted carbapenems (2).

Pt 2 (n-C 6 H 13 CS 2 ) 4 cristallise dans le systeme monoclinique avec le groupe d'espace C 2 /c. Affinement de la structure jusqu'a 0,081