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91.
Total syntheses of iso‐cladospolide B ( 1 ) and the 12‐membered macrolactone (6S,12R)‐6‐hydroxy‐12‐methyloxacyclododecane‐2,5‐dione ( 2 ), a non‐natural product, were achieved from a common intermediate starting from commercially available 1,9‐nonane diol.  相似文献   
92.
Electrophilic cyclizations of unactivated alkenes play highly important roles in the synthesis of useful building blocks. This account describes our contributions to the rational design of monofunctionalized chiral Lewis base catalysts for enantioselective iodo‐ and protocyclizations. For the stereoselective promotion of electrophilic bromocyclizations, nucleophilic phosphite–urea cooperative catalysts have been designed.  相似文献   
93.
A formal total synthesis of palmerolide A has been accomplished by assembling three fragments by means of successive Julia–Kocienski olefination, Yamaguchi esterification, and ring‐closing metathesis (RCM). Our initial efforts to combine the first two fragments through a Julia–Kocienski reaction between a secondary sulfone and a ketone were not successful; nevertheless, it was feasible between a primary sulfone and aldehyde. Yamaguchi esterification with the third fragment then set the stage for a RCM reaction. Initial failure of the RCM with a PMB‐ether adjacent to the olefins and the difficulty in cleaving the PMB‐ether prompted us to change the choice of protecting groups, which then paved the way to the macrocyclic core of palmerolide A.  相似文献   
94.
The gibberellins (GAs) are a group of naturally-occurring tetracyclic diterpenoid plant growth hormones which are widely present in higher plants and some fungal species. To date over one hundred GAs have been identified and found to be involved in almost every aspect and stage of the growth and development of plants1.Among the GAs identified to date, gibberellic acid (GA3) 1 is the most active and widely used naturally occurring gibberellin. However structure-activity relationship studies …  相似文献   
95.
The paper illustrates two efficient routes to macrolactone 19 containing a 3-(para-methoxybenzyloxy)propyl side chain at C-15. The chiral center at C-15 was introduced by a Noyori reduction of keto ester 5. The intermediate common to both routes, aldehyde 8, was prepared from keto ester 5. The subsequent chain extension utilized Evans aldol reactions. The first route leads to the alkene 14, which was used, after hydroboration, for a Suzuki cross-coupling reaction with vinyl iodide 15. The derived seco acid 18 was converted into the macrolactone 19 by a Mitsunobu lactonization by using immobilized triphenylphosphine. Alternatively, an aldol reaction of 8 with the 4-pentenoyl derivative 20 was used to prepare alkene 26. This building block led to ester 28, which could also be converted into macrolactone 19 by the classical ring-closing metathesis. After conversion of the C-15 side chain to the corresponding aldehyde, the enamide was introduced through hemiaminal formation and formal elimination of water. Separation of the double-bond isomers and removal of the silyl protecting groups provided salicylihalamides A (E)-1 and B (Z)-1.  相似文献   
96.
The reaction of cyclic γ,δ-epoxy esters with p-toluenesulfonic acid monohydrate is described. The reaction carried out in benzene or methylene chloride gave tosyloxy lactones as product. The ethoxy or methoxy lactones were obtained when ethanol or methanol were used as solvent. A mechanism of this lactonization is proposed.  相似文献   
97.
Herein, we describe a concise assembly of central 6,8-dioxabicyclo[3,2,1]octane core of didemniserinolipid by employing a Pd-mediated alkynediol cycloisomerization and a formal total synthesis of didemniserinolipid B.  相似文献   
98.
A chiral pool approach starting with d-glucose, using the Yamaguchi protocol and a Z-selective HWE reaction followed by lactonization, has been applied to execute the total synthesis of strictifolione.  相似文献   
99.
The titled compound 6a and 6b were synthesized from tricyclic ketone 1 through five steps.  相似文献   
100.
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