摘要:

A Contribution to the Stereochemistry of theS′E‐Reaction: the Protonation of an Optically Active 1, 1‐Disilyl‐2‐alkeneAn optically active, 1, 1‐disilyl‐2‐alkene2was reacted with CF3COOH and HBF4·OMe2and furnished with loss of one silyl group and migration of the double bond the corresponding vinylsilane4. Determination of the absolute configuration and enantiomeric excess of2and4showed theS′E‐reaction to proceed in the case of CF3COOH with 48% (74%anti/26%syn) and in the case of HBF4·OMe2with 44% (72%anti/28%syn) stereoselectivity. Deuteriodesilylation with CF3COOD resulted in the exclusive formation of at C (3)‐monod

ISSN:0018-019X    

DOI:10.1002/hlca.19830660112

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

A careful deformation density study of tetrafluoroterephthalodinitrile at 98K has been made from X‐ray diffraction measurements. Prominent ‘bonding density’ peaks are found at or near the mid‐points of the C, C‐ and C, N‐bonds but not for the C, F‐bonds, which show only weak density. Similarly weak bonding densities for C, F‐bonds are also found for 1, 1, 4, 4‐tetrafluorocyclohexane. The possible significance of these results in terms of bonding theory is

ISSN:0018-019X    

DOI:10.1002/hlca.19830660113

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

The crystal structure of 1,1,4,4‐tetrafluorocyclohexane has been determined from X‐ray diffraction measurements at 95 K. Internal motion of the CF2‐group can be discerned from analysis of the atomic vibration tensors. The pattern of bond lengths suggests that an anomeric‐effect type of interaction between antiperiplanar C,C‐ and C,F‐bonds (as well as between C,H‐ and C,F‐bonds) may be operative i

ISSN:0018-019X    

DOI:10.1002/hlca.19830660114

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

High‐resolution ESR. spectra of the radicals CH2COOR, CH3CHCOOR and (CH3)2CCOOR with RCH3, CH2CH3, CH(CH3)2and C(CH3)3in liquid solution confirm planar energy‐minimum structures with substantial barriers to internal rotation about the Ċ, CO‐bonds (⋍40 kJ/mol) and partial π‐electron delocalization. The assignments of coupling constants to protons in isomeric positions and the conclusions on radical structures are supported by INDO

ISSN:0018-019X    

DOI:10.1002/hlca.19830660115

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

The Synthesis of 2,3,4,5‐1H‐Tetrahydroimidazo[2,1‐b]quinazolin‐2,5‐diones and analogous 2,3,4,5‐1H‐Tetrahydroimidazo[1,2‐a]thieno[2,3‐d] (or [3,2‐d])‐pyrimidin‐2,5‐dionesThe syntheses of various imidazo [2, 1‐b]quinazolinediones and their thio

ISSN:0018-019X    

DOI:10.1002/hlca.19830660116

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

A conformational study was carried out on Boc‐(L‐Val‐D‐Val)6‐OMe in the crystalline state by X‐ray and IR. and by1H‐NMR. in chloroform. The dodecapeptide crystallizes from CHCl3/EtOAc with a left‐handed helical structure of the type ↑↓ β5.6, and from CHCl3/MeOH (or MeOH) with a different structure. In chloroform it forms three slowly interconverting species: one is a ↑↓ β5.6left‐handed helical species, and the other two are most likely single‐stranded β4.4helical species of opposite handedness. The double‐stranded helical species is predominant in fresh solutions of samples obtained from CHCl3/EtOAc. Because of the slow conversion or formation of this species some hours are needed to reach the conformational

ISSN:0018-019X    

DOI:10.1002/hlca.19830660117

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

Reductive elimination at 1,2exo‐diiodonorbornane (6) was induced byCollman'sreagent. Surprisingly, 1,2endo‐diiodonorbornane (9) and 1‐iodo‐2endo‐trifluoromethylsulfonyloxy‐norbornane (10b) lead only to reactions of the substituent in 2‐position. Mechanistic aspects are related to the reactions of monosubstituted iodonorbornanes withCol

ISSN:0018-019X    

DOI:10.1002/hlca.19830660118

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

Acetylacetonatorhodiumolefin systems, allylrhodium complexes, or (Ph3P)3RhCl catalyzed the conversion of alkenes and molecular oxygen to carbonyl compoundsviaCC‐bond cleavage. For example, 2,3‐dimethyl‐2‐butene was transformed into acetone. Butadiene and isoprene also undergo oxidative CC‐bond cleavage to form acrylaldehyde and rela

ISSN:0018-019X    

DOI:10.1002/hlca.19830660119

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

Reaction of cobaltocene with cyclopentadiene and air results in the formation of the title compound; its structure has been elucidated by spectroscopic and X‐ray method

ISSN:0018-019X    

DOI:10.1002/hlca.19830660120

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

Structural modifications of testosterone and 19‐nortestosterone have led to the synthesis of over 60 androstane and estrane derivatives whose sensory evaluation has allowed molecular parameters to be established for release of a ‘steroid‐type’ scent. Odor perception with O‐containing compounds in both classes has been found to beregioselective. Osmophoric groups at C(3) were found to be the most active and specific. Functionality at C(2) is accompanied to a large extent by anosmic defects, and O‐containing substituents at C(1) and C(4) appear to affect the receptor membrane in exceptional cases.A further characteristic of the ‘steroid‐type’ scent isdiastereoselectivity. The odor intensity of axial 2‐ and 3‐hydroxysteroids is far greater than that of the equatorial epimers, and epimeric hydroxy‐groups in the 1‐, 4‐, and 5‐positions lead to almost complete absence of odor. In addition, only steroids with ‘normal’ ring junctions and configuration were found to be odorants, whereas compounds withcis‐junctions between rings A and B, or C and D, were found to be practically inactive, Steroids therefore folow the ‘triaxial rule of odor sensation’.The most remarkable feature of our findings with steroid odorants isenantioselectivityThe term ‘regioselective’ is currently used for a reaction in which formation of one structural (or positional) isomer is favored over another. For convenience we use ‘regioselective’, ‘diastereoselective’ or ‘enantioselective’ for substrate‐receptor interactions in which one positional isomer, diastereoisomer or enantiomer leads to a different sensory response (in quality and/or intensity) than another.. Whereas with C19‐steroids of the ‘natural’ enantiomeric series the perception threshold is extremely low (<6 ppb), the corresponding ‘unnatural’ enantiomers have been found essentially odorless by a panel of 30 persons. This appears to be the first r

ISSN:0018-019X    

DOI:10.1002/hlca.19830660121

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY