The synthesis of simple alkyl substituted spiroacetals by α,α′-alkylation of metalated acetone dimethylhydrazone with appropriate electrophiles and subsequent acid catalyzed cleavage and ring closure of the products is described.
Cyclische Ether als Edukte zur Synthese von Schmetterlings-Pheromonen
作者:Helmut Poleschner、Matthias Heydenreich、Dieter Martin
DOI:10.1055/s-1991-28425
日期:——
Cyclic Ethers as Educts for the Synthesis of Lepidoptera Pheromones Ï-Iodo(trialkylsiloxy)alkanes 2 prepared by ring opening of cyclic ethers with iodotrimethylsilane, are useful starting materials for the synthesis of pheromone components. Reaction with triphenylphosphine to give the corresponding Wittig reagent and subsequent coupling with lithium (Z)-dihex-1-enylcuprate gives (Z)-alken-1-ols 5 and 7, after deprotection, in good yields. The direct coupling of 2 with alkynes failed because of competition reactions, however, the more stable Ï-iodo-1-(tert-butyldimethylsiloxy)alkanes were able to undergo C,C-coupling with alkynes. The thus formed 1-(tert-butyldimethylsiloxy)-5-decyne (13c) was hydrogenated and deprotected to give (E)-5-decen-1-ol (15c).
Highly Efficient and Broad-Scope Protocol for the Preparation of 7-Substituted 6-Halopurines via N9-Boc-Protected 7,8-Dihydropurines
作者:Dalimil Dvořák、Vladislav Kotek、Tomáš Tobrman
DOI:10.1055/s-0031-1290068
日期:2012.2
9-Boc-6-chloropurine, which can be obtained in high yield, is nearly quantitatively reduced with the THFËBH3 complex. The obtained 9-Boc-7,8-dihydropurine derivative is more stable compared to the corresponding 9-tritylpurine and can be smoothly N7-alkylated, acylated, or it can serve as an N-nucleophile in conjugate additions. Deprotection with trifluoroacetic acid followed by MnO2 oxidation affords the N7-substituted purines in high yields. The whole sequence of alkylation, deprotection, and oxidation can be done with crude intermediates using chromatography only for the purification of the final N7-substituted purine.
An intramolecular Diels-Alder approach to the synthesis of the right hand half of the ionophore antibiotic X-14547A
作者:Martin P. Edwards、Steven V. Ley、Simon G. Lister
DOI:10.1016/0040-4039(81)80099-8
日期:1981.1
Starting from ethylbutyrate, an efficient synthesis of the right hand half of the antibioticX-14547A has been achieved in which the desired five relative chiral centres were created by an intramolecular Diels-Alder reaction.
Similarly, the C-O bond of 1,3-oxazolidine rings cleaved to give ring-opened imine or enamine derivatives. The reactions of aromatic ketone ethylene acetals and cyclohexanone trimethylene acetal led to deprotection of the acetal unit to liberate free ketones. With reagent 1b, cycloalkanone ethylene acetal afforded a dimeric product with 2-iodoethyl alkenoate moieties, while aromatic ketone ethylene