摘要:

Abstract3‐amino‐2H‐azirines undergo a number of ring opening reactions. The cleavage of the azirine‐N(1), C(3) double bond leads thereby to synthons which can be considered as amino acid equivalents. The reaction of 3‐amino‐2H‐azirines with carboxylic acids yields N‐acyl amino acid amides, which can be converted by a selective amide cleavage to the corresponding N‐acyl amino acids. 2‐Oxazolin‐5‐ones are intermediates of this amide cleavage. This reaction sequence has been used for the extension of peptide chains as well as for a number of heterocycle syntheses. Likewise, the described synthesis of cyclic depsipeptides and lactones by direct amide cyclization proceeds via 2‐oxazolin‐5‐one intermediates. The selective amide cleavage was also applied to a novel method for the resolution of enanti

ISSN:0021-2148    

DOI:10.1002/ijch.198600002

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractNucleophilic ring opening of three‐membered rings is discussed in terms of leaving group basicity. Reactions of activated (weakly basic leaving groups) 2,2‐dimethylaziridines 5 and 2‐phenylaziridines 6 with alcohols ROH are studied with reference to the site selectivity of ring opening and competing side‐reactions. Abnormal opening (at the substituted carbon) of 5 proceeds in neutral ROH without catalyst when the activation is strong (tosyl) whilst no reaction or mainly carbonyl attack is observed with weak activation (CONHAr). NaClO4catalyzes the abnormal opening of 5. EtO−gives exclusively normal opening of 5 whilst, in contrast to the literature, MeO−gives also a substantial amount of abnormal ether. Attack on 6 always occurs at both positions with the predominance of the abnormal reaction being greater for MeO−than for EtO−. These reactions are considered SN2 with steric and benzylic differentiation between normal and abnormal attack depending on the size of ROH. Acid catalyzed openings of 5 and 6 proceed exclusively abnormally in the ether‐forming reaction as well as in side‐reactions. Competition experiments and increase of the side‐reactions with the size of ROH demonstrate a deceleration of the ether‐forming reaction with the size of ROH. Obviously, the side‐reactions originate from a carbenium ion whilst the ethers are mainly formed by a borderline mechanism. R(‐)6b and acidic MeOH give only 8% racemization in the abnormal ether. An order of activation is proposed for activated aziridines under acid ca

ISSN:0021-2148    

DOI:10.1002/ijch.198600003

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

Abstract3‐Halobithienyls have been prepared through the Pd(PPh3)4‐catalyzed coupling of thiopheneboronic acids with 2,4‐dihalothiophenes. The ring‐opening of the corresponding 3‐lithiobithienyls obtained upon halogen‐metal exchange with phenyllithium has been investigated. Compound12, 3′‐iodo‐2,2′,2″‐terthienyl, was prepared in one step through the Pd(PPh3)4‐catalyzed coupling of two equivalents of 2‐thiopheneboronic acid with 2,3,5‐triiodothiophene. Treatment of12with phenyllithium and methyl iodide gave a mixture of compounds10and11occurring

ISSN:0021-2148    

DOI:10.1002/ijch.198600004

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractBamberger ring cleavage acylation of N‐p‐toluenesulfonyl (tosyl) histamine followed by hydrogenation yields 3,4‐diacylaminobutanetosylamine, a triamine containing groups with different chemical reactiv

ISSN:0021-2148    

DOI:10.1002/ijch.198600005

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractRegiocontrolled deprotonation (e.g. lithiation) of 3‐methyl‐4‐H‐5,6‐dihydro‐1,2‐oxazine 1 is achieved at −65°C. The lithiated compound reacts cleanly with the halogens Cl2, Br2and I2at low temperatures (−65°C) to give the corresponding 4‐halo derivatives. Reaction of the 4‐iodo compound2awith KF in diethyleneglycol gives the elimination product4whereas the bromo compound2breacts under substitution to the 4‐fluoro derivatives 5. The fluorooxazine derivatives 8a‐c were converted to the αfluoroenones 11 a‐cviathe oxoiminium salts 10a‐c. The U.V. and1HNMR of the novel series of

ISSN:0021-2148    

DOI:10.1002/ijch.198600006

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractCoumarins 1–5 were reacted with O2in aprotic media. The course of the reaction was followed by using methyl iodide to “Cap” (trap) the oxy‐anions generated. Abstraction of the enolic hydrogen (where available) proved to be the most facile process followed by “saponification” of the lactone linkage. Thecis‐stereochemistry of the original coumarin was maintained allowing easy access to a variety of o‐coumarin

ISSN:0021-2148    

DOI:10.1002/ijch.198600007

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractA new synthetic approach to vinylphosphonates is presented. The reaction of diethyl benzoylphosphonate (1) with diethyl methoxycarbonyl‐methyl‐phosphonate (2) gives diethyl 2‐methoxycarbonyl‐l‐styrylphosphonate (3) as a mixture of geometrical isomers (Z‐3) and (E‐3) in the ratio of 83:17. In contrast, reaction of1with the heterocyclic phosphonate reagent, 2‐methoxycarbonyl‐methyl‐2‐oxo‐4,5‐dimethyl [1,3,2] dioxaphospholane (4) leads to a mixture of the isomers (Z‐3) and

ISSN:0021-2148    

DOI:10.1002/ijch.198600008

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractA variety of chiral 2,4‐disubstituted‐5‐trifluoroacetamido‐,5‐carbobenzyloxyamino, and 5‐β,β,β,‐trichloroethoxycarbonylaminooxazoles have been prepared from diamide, dipeptide, or amide nitrile precursors. Conversion to their (poly)amide equivalentsviaa deacylation/hydration sequence is described. The extent of induction of chirality realized upon ring opening in each case is de

ISSN:0021-2148    

DOI:10.1002/ijch.198600009

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractA facile synthesis of the pyrrolizidine alkaloids, (±)‐supinidine (14) and (±)‐trachelanthamidine (8) was achieved by employing aziridine as the reactive sp

ISSN:0021-2148    

DOI:10.1002/ijch.198600010

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractA new synthesis of 4‐ and 7‐carbon‐substituted indoles is described. The overall sequence involves the addition of a nitrile oxide to 1 carboethoxy‐2‐(or 3‐) allylpyrrole, hydrogenation of the intermediate isoxazoline toβ‐hydroxy ketone and cyclization of the ketol using magnesium or zinc triflate to the substituted indole. This new indole‐forming strategy can also accommodate the introduction of oxygen functionality into the indole 6‐position. Possible mechanistic aspects of the rea

ISSN:0021-2148    

DOI:10.1002/ijch.198600011

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY