ISSN:0021-2148    

DOI:10.1002/ijch.198900017

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

ISSN:0021-2148    

DOI:10.1002/ijch.198900018

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractA stereospecific18O‐labelling study shows that thesyn‐hydroxy group is preferentially lost from thesyn, anti‐title diol uponi‐C4H10chemical ionization, indicating occurrence of a stereoelectronic effect in this process. A collision‐induced dissociation study of deuterium‐ and18O‐labelled analogs shows that a symmetrical ether structure is not formed in the above process by an SNi mechanism. This result leads to the conclusion that the stereoelectronic assistance of theanti‐OH group in the loss of thesyn‐hydroxyl is expressed either in a weak transition state interaction or by other processes such as β‐elimination via hydrogen transfer with concomitant d

ISSN:0021-2148    

DOI:10.1002/ijch.198900019

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe crystal structures ofcis‐1,6‐cyclodecanediol (1) and of the molecular compound formed betweencisandtrans‐1,6‐cyclodecanediol in the ratio 2:1 (2) have been established by X‐ray diffraction. The two substances are closely isostructural. (Crystal data: both monoclinic, P21/c, Z = 6; (1)a= 6.665(6),b= 18.074(3),c =14.351(8) Å, β = 119.77(6)°,V= 1500(2) Å3; (2)a= 6.679(8),b =18.074(4),c= 14.314(10) Å, β = 119.64(8)°,V= 1502(3) Å3). The asymmetric unit of the molecular compound contains onecismolecule in a general position and onetransmolecule at a center of symmetry. In the crystal of the purecisdiol a set of disorderedcismolecules mimics the corresponding centrosymmetrictransmolecules in the molecular compound. The molecules have the stable BCB cyclodecane ring conformation, except for the disorderedcismolecules, which have a conformation about 2 kJ mol−1higher in energy (molecular mechanics calculations). The intricate three‐dimensional hydrogen‐bond network found in both crystals is presumably especially favorable from

ISSN:0021-2148    

DOI:10.1002/ijch.198900020

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe reduction‐rearrangement chemistry of two rigidly held doubly vinylogous β‐diketones has been investigated. One hydrophenanthrene dienedione was a tricyclic intermediate in the Wilds total steroid synthesis and the other was prepared from the Wieland‐Miescher ketone. Lithium‐ammonia reduction yielded a cyclopropanedione and a cyclopropanoketol, respectively. Treatment of these compounds with acid furnished cyclopropane‐cleaved

ISSN:0021-2148    

DOI:10.1002/ijch.198900021

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe geometries of trimethylenetriasterane1, triasteranetrione2, and trispirocyclopropanetriasterane3have been determined by X‐ray crystal structure analyses. All three compounds have D3hsymmetry and contain two skeletal cyclopropane rings which are symmetricallycis‐trisubstituted. The vinyl and the carbonyl substituents in1and2apparently exert about the same acceptor effect on the central cyclopropane rings and cause a small but significant lengthening of the endocyclic C‐C bonds (1.517 Å in1and in2) in comparison to an average normal bond length in cyclopropanes of 1.508 Å, while in3no effect of the spirocyclopropane groups on the bond length in the central rings (1.506 Å) is evident The vinylcyclopropane and bicyclopropyl subunits in1and3respectively are ideally antiperiplanar and almost undistorted with respect to the parent hydrocarbons as evidenced by the bond angles and13C‐13C coupling consta

ISSN:0021-2148    

DOI:10.1002/ijch.198900022

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe syntheses of the new hydrocarbons trimethylenetriasterane12, trispirocyclopropanetriasterane3, trispirocyclopropanenortricyclane4, and of the trispirocyclopropanenorbornanes5, 6, and7are reported.12contains six vinylcyclopropane units rigidly held in an antiperiplanar (ap) conformation in aD3hsymmetric framework.3and4are the first model compounds with bicyclopropyl units rigidly fixed in ans‐trans(ap) conformation (Θ = 180°). Their PE spectra reveal that the interaction parameter βww= −1.73 eV for this arrangement is the same as that for

ISSN:0021-2148    

DOI:10.1002/ijch.198900023

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractA pair of isodicyclopentafulvenes that carries an exocyclic phenyl group para‐substituted with an aza‐15‐crown‐5 or aza‐18‐crown‐6 ring has been prepared. These molecules (5aand5b) and their respective NaClO4(11) and KSCN (12) complexes were examined for the extent of π‐facial stereoselectivity operational during their Diels‐Alder cycloaddition to (Z)‐1,2‐bis(phenylsulfonyl)ethylene (2) under conditions of high pressure. Whereas5aand5bengage in [4 + 2] condensation with a 2.5–3.1 preference for dienophile capture from the above‐plane direction, their complexes show a substantially reduced tendency for doing so(14/13= 1.2–1.4). However, this response goes contrary to those para‐substituent effects previously observed. The linear correlation noted earlier conformed to anincreasedpreference for above‐plane cycloaddition to2as the para‐substituent became progressively more electron‐withdrawing. Probable reasons for this seemin

ISSN:0021-2148    

DOI:10.1002/ijch.198900024

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe first three title compounds were prepared by treating the diastereomeric 4‐t‐butyl‐1‐phenyl‐1‐phenylthiocyclohexanes8or9(Scheme 3) with lithium, sodium, or potassium naphthalenide, respectively. The potassium derivative was also obtained by treatment of9with sodium/potassium alloy and the cesium derivative was similarly obtained by reaction with cesium/potassium/sodium alloy. Quenching of any of these salts with D2O gavecis‐andtrans‐4‐t‐butyl‐1‐phenylcyclohexane‐1‐d(cis‐andtrans‐7‐d) in an approximately 1:1 ratio. The reaction was stereoconvergent and the product ratio independent of the metal; the result is explained in terms of a diffusion controlled reaction of a planar or near‐planar carbanion. In contrast, methylation with methyl iodide gave the product of axial methylation 10 in an approximately 2:1 predominance over diastereomer11. This result is explained in terms of Curtin‐Hammett kinetics involving a stereoelectronically preferred axial approach to the electrophile.13C NMR spectral studies of the lithium, potassium, and cesium salts indicate extensive delocalization of the anionic charge into the ring—somewhat more so with the K and Cs than with the Li salt. This finding supports the hypothesis that at least the K and Cs salts involve a planar carbanion moiety, whereas the Li salt may be slightly nonplanar. Both spectrally and stereochemically, the title compounds differ substantially from the

ISSN:0021-2148    

DOI:10.1002/ijch.198900025

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractSeveral mono‐ and di‐O‐alkyloximes have been regioselectively transformed to thesyn α‐lithio derivatives by treatment withn‐butyllithium. The control of oxime ether geometry served to control regioselectivity in α‐lithiation and subsequent carbon‐carbon (alkylation, oxidative coupling) and carbon‐halogen bond formation reactions. The geometry‐directed α‐lithiation‐dimerization sequence was used for the synthesis

ISSN:0021-2148    

DOI:10.1002/ijch.198900026

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY