ISSN:0018-019X    

DOI:10.1002/hlca.19920750202

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe use of α,α,α′,α′ ‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols ( = TADDOLs;1) as chiral NMR shift reagents (1H,13C,19F) is described. In many cases, the ratio of enantiomeric alcohols and amines can be determined under standard conditions of measurement (CDCl3as solvent, room temperature). The preparation and use of a new type of TADDOL, the tetrakis(dimethylamino) derivative1d, is described. Menthol, octan‐2‐ol, and oct‐1‐yn‐3‐ol are partially resolved by crystallizat

ISSN:0018-019X    

DOI:10.1002/hlca.19920750203

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractReactions of monosubstituted alkenes RCH = CH2and [Re(η5–C5H5)(CH2Cl2) (NO)(PPh3)]+BF 4−give complexes ([Re(η5–C5H5))(CH2CHR)(NO) (PPh3)]+BF 4−(1a–g) in 63–99% yields as mixtures of (RS,SR)‐ and (RR,SS)‐diastereoisomers (1a(R = Me), 66:34;1b(R = Pr), 63:37;1c(R = PhCH2), 70:30;1d(R = Ph), 75:25;1e(R = i‐Pr), 64:36;1f(R =t‐Bu), 84:16;1g(R = Me3Si), 69:31;Scheme 2). These differ in the CC enantioface bound to the chiral Re fragment. In most cases, the analogous reactions of RCHCH2and [Re(η5–C5H5) (C6H5Cl)(NO)(PPh3)]+BF 4+give comparable results. When1a–e,gare heated in PhCl at 95–100°, equilibration to 96:4, 97:3, 97:3, 90:10,>99:99:<1 (RS,SR)/(RR,SS) mixtures occurs (79–99% recoveries;Tables 1and2). Thus, thermodynamic enantioface‐binding selectivities are much higher than kinetic binding selectivities. This phenomenon is analyzed in detail. A crystal structure of (RS,SR)‐1e(monoclinic,P21/c,a= 10.256(1) Å.b= 17.191(1) Å,c= 16.191(1) Å, β = 101.04(1)°, Z = 4) shows that the Re–C(1)–C(2) plane (seeFig.2) is nearly coincident with the Re–P bond (angle 15

ISSN:0018-019X    

DOI:10.1002/hlca.19920750204

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Synthesis and Behaviour of Isoflavones Substituted in 2′‐PositionThe protected chalcones6–8prepared from acetophenone and benzaldehydes rearranged to the dimethoxypropanone derivatives9–11in the presence of trimethyl orthoformate by Tl(NO3)3. 3 H2O. These compounds could be cyclized to the isoflavones12–14in high yields (Scheme 2). The conversion of these isoflavones to the corresponding isoflavanes (model compounds of the phytoalexin glabridin; seeScheme 1) was the main goal of this work. Hydrogenation of13and14gave the isoflavanes15and16, respectively and their deprotection the racemic natural product 4′‐O‐demethylvestitol (17). Reduction of13and14yielded different compounds depending on the reducing agent (Scheme 3). The saturated alcohols20–23could be obtained with NaBH4or LiBH4. They were transferred into the racemic9‐O‐demethylmedicarpin (24) and haginin D (25) under acidic conditions. The ketones26–28(Scheme 4) were obtained in high yields by reduction of12–14with DIBAH. Deprotection of26yielded the racemic 2,3‐dihydrodaidzein (29). Compounds13and27as well as20and22showed different behaviour under reduction conditions with Li in liquid ammonia. An efficient method for the introduction of the MeOCH2O and the MeOCH2CH2OCH2protecting groups into hydroxylated benzaldehydes and acetophenones (Scheme 5) is described. The appropriate experimental conditions depend on the regioselectivity and on the number of the protected groups. The protected aldehydes, especially those with a protectedorthoOH group, show an extraordinary ionization behaviour in chemical‐ionization mass spec

ISSN:0018-019X    

DOI:10.1002/hlca.19920750205

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe chemical syntheses of the phosphorothioate of (2′–5′)adenylate dimer (see6a,6b) and trimer (see11a,11b,12a,12b) as well as of their 5′‐monophosphates (see15a,15b,16a,16b) using the phosphoramidite method are described. The resulting diastereoisomer mixtures were separated into the pure components by chromatographical means. All synthetic intermediates were characterized by TLC, elemental analysis, and UV and1H‐

ISSN:0018-019X    

DOI:10.1002/hlca.19920750206

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reaction of 9‐bromoanthracene (1) with benzenethiol(ate) in tetraglyme proceeds by aSNAr mechanism. The concurrent formation of anthracene is not due to a competing single‐electron‐transfer pathway involving either benzenethiol or benzenethiolate

ISSN:0018-019X    

DOI:10.1002/hlca.19920750207

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractA synthetically useful CC bond formation involving the photochemical addition of quinoxaline‐2(1H)‐thiones to alkenes is described. Irradiation of the quinoxaline‐2(1H)‐thiones1–4in the presence of the alkenes7gave the 2‐(2′‐mercaptoalkyl)quinoxalines8–11in moderate‐to‐good yieldsviaring cleavage of an intermediate aminothietane with aromatization of the quinoxaline ring. The latter was formed by [2+2] photocycloaddition of the CS bond of the quinoxaline‐2(1H)‐thione a

ISSN:0018-019X    

DOI:10.1002/hlca.19920750208

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractIntramolecular cyclisation of properly protected and activated derivatives of 2′,3′‐secouridine ( = 1‐{2‐hydroxy‐1‐[2‐hydroxy‐1‐(hydroxymethyl)ethoxy]‐ethyl}uracil;1) provided access to the 2,2′‐, 2,3′‐, 2,5′‐, 2′,5′‐, 3′,5′‐, and 2′,3′‐anhydro‐2′,3′‐secouridines5, 16, 17, 26, 28, and31, respectively (Schemes 1–3). Reaction of 2′,5′‐anhydro‐3′‐O‐(methylsulfonyl)‐ (25) and 2′,3′‐anhydro‐5′‐O‐(methylsulfonyl)‐2′,3′‐secouridine (32) with CH2CI2in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene generated the N(3)‐methylene‐bridged bis‐uridine structure37and36, respectively (Scheme 3). Novel chiral 18‐crown‐6 ethers40and44, containing a hydroxymethyl and a uracil‐1‐yl or adenin‐9‐yl as the pendant groups in a 1,3‐cisrelationship, were synthesized from 5′‐O‐(triphenylmethyl)‐2′,3′‐secouridine (2) and 5′‐O,N6‐bis(triphenylmethyl)‐2′,3′‐secoadenosine (41) on reaction with 3,6,9

ISSN:0018-019X    

DOI:10.1002/hlca.19920750209

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe l‐azabicyclo[2.2.1]heptan‐3‐exo‐ol (2) was resolved by fractional crystallisation of its hydrogen tartrate salts. The enantiomers (+)‐ and (−)‐2were oxidised to the ketones (−)‐4and (+)‐4, respectively (Scheme). CD spectroscopy suggested that (−)‐4possesses the (1R,4S)‐configuration. This absolute configuration was confirmed by single‐crystal X‐ray diffraction of the derivative (+)‐(1R,4R)‐3‐(1,3‐dithian‐2‐ylid

ISSN:0018-019X    

DOI:10.1002/hlca.19920750210

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reaction oftrans,trans‐[WH(CO)2(NO)(PMe3)2] (1) with (pyridin‐2‐yl)‐substituted aldehydes and ketones, (pyridin‐2‐yl)C(O)R where R = H, Me, Ph, pyridin‐2‐yl, and with 6‐methylpyridine‐2‐carbaldehyde was studied. In all cases, facile insertion of the CO bond into the WH bond was observed, with rapid subsequent extrusionof a coordinated CO ligand affordingO,N‐bidentate coordinated tungsten alkoxides. Only in case of pyridine‐2‐carbaldehyde and di(pyridin‐2‐yl) ketone, the initialn1O‐bonded insertion product could be observed as unstabl

ISSN:0018-019X    

DOI:10.1002/hlca.19920750211

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY