ABSTRACT
Ring opening with organometallic reagents of [2.2.2]-acylnitroso cycloadducts, including an enantioselective kinetic resolution of these compounds, has been accomplished for the first time. By the careful choice of reaction conditions, it was possible to obtain new cyclohexenyl hydroxamic acids with complete anti-stereoselectivity and a nice regioalternating control. A remarkable effect of the halogen of the Grignard reagent was observed during ring opening.
Subject(s)
Copper/chemistry , Nitroso Compounds/chemistry , Alkylation , Catalysis , Indicators and Reagents/chemistry , Stereoisomerism , Substrate SpecificityABSTRACT
A mild ring opening of vinyl epoxides and aziridines with B(2)Pin(2) catalyzed by Ni(0)-Binap affords new functionalized allylic boron derivatives which undergo sequential transformations. The uncatalyzed allylation of aldehydes allows obtaining challenging bishomoallylic alicyclic 1,3-diols and 1,3-amino alcohols with remarkably high stereoselectivities. Valuable trans-bisallylic 1,4-amino alcohols can be obtained by a simple oxidation.
Subject(s)
Aziridines/chemistry , Boron Compounds/chemical synthesis , Epoxy Compounds/chemistry , Nickel/chemistry , Vinyl Compounds/chemistry , Boron Compounds/chemistry , Catalysis , Combinatorial Chemistry Techniques , Molecular Structure , StereoisomerismABSTRACT
The glycosylation of alcohols by the new diastereoisomeric d,l-6-deoxy-N-Cbz-imino glycal-derived allyl N-nosyl aziridines 5 and 6 affords, after deprotection of the 4-(N-nosylamino) group, the corresponding 2,3-unsaturated-N-Cbz-imino-O-glycosides bearing a free amino group on C(4) through a completely 1,4-regio- and substrate-dependent stereoselective glycosylation process.
Subject(s)
Aminoglycosides/chemical synthesis , Aziridines/chemistry , Glycosides/chemical synthesis , Imino Sugars/chemistry , Alcohols/chemistry , Aminoglycosides/chemistry , Glycosides/chemistry , Glycosylation , Molecular Structure , StereoisomerismABSTRACT
The regioselective ring opening of 2-aryl-substituted four-membered heterocyclic rings with phenols, including catechol, was achieved by the use of aryl borates in mild and neutral reaction conditions without the aid of any transition metal catalysts. While N-alkyl azetidines were found not to be reactive, optically active N-tosyl azetidines gave the corresponding beta-aryloxy amines in a racemic form, thus indicating the considerable carbocationic character of the transition state. The introduction of a hydroxyl group in the azetidine ring (i.e., an azetidinol), able to anchor the aryl borate and to direct the subsequent nucleophilic delivery, was shown to determine the ring-opening process with predominant inversion of configuration. When enantiomerically enriched 2-aryl oxetanes were used, the reduced extent of racemization observed (up to 93:7 er) was rationalized by an intramolecular delivery through a six-membered transition state, giving beta-aryloxy alcohols with a predominant retention of configuration (i.e., a syn-stereoselective ring opening). The aryloxy alcohols obtained, endowed with suitable functionalities, can be cyclized to give access to enantiomerically enriched 2-aryl-1,5-benzodioxepins.
Subject(s)
Azetidines/chemistry , Borates/chemistry , Ethers, Cyclic/chemistry , Benzoxepins/chemistry , Phenols/chemistry , Stereoisomerism , Substrate SpecificityABSTRACT
The first successful asymmetric transfer of rhodium-alkynyl species to symmetrical strained alkenes has been realized starting from bicyclic hydrazines and alkynylboronic esters.
Subject(s)
Boronic Acids/chemistry , Bridged Bicyclo Compounds/chemistry , Esters/chemistry , Hydrazines/chemistry , Rhodium/chemistry , Catalysis , Stereoisomerism , Substrate SpecificityABSTRACT
A novel and simple method for the stereoselective synthesis of substituted 3-aryl-2,3-dihydrobenzofurans by intramolecular cyclization of hydroxyphenols is described. The stereoselective ortho-C-alkylation of phenols allows a novel and stereoselective access to a diverse array of polyfunctionalized products containing a diarylmethane stereogenic center without the need for time-consuming protection-deprotection steps.
Subject(s)
Benzofurans/chemical synthesis , Phenols/chemistry , Cyclization , Epoxy Compounds/chemistry , StereoisomerismABSTRACT
A chemo-, regio-, and stereoselective direct carbon-carbon coupling of readily available aryl borates with N-protected aryl aziridines provides a method for the synthesis of new 2-(o-hydroxyaryl)-2-aryl ethylamines which can be used, in a novel annulation sequence, to give stereodefined substituted 3-aryl indolines. [reaction: see text]
ABSTRACT
A conceptually new, simple and practical method for the syn-nucleophilic displacement of aryl and vinyl epoxides and aryl aziridines with (substituted) phenols, using aryl borates as activating nucleophiles under neutral conditions, is reported.
