Pd-Catalyzed Intramolecular Aminohydroxylation of Alkenes with Hydrogen Peroxide as Oxidant and Water as Nucleophile
摘要:
A palladium-catalyzed intramolecular aminohydroxylation of alkenes was developed, in which H2O2 was applied as the sole oxidant. A variety of related alkyl alcohols could be successfully obtained with good yields and excellent diastereoselectivities, which directly derived from oxidation cleavage of alkyl C-Pd bond by H2O2. Facile transformation of these products provided a powerful tool toward the synthesis of 2-amino-1,3-diols and 3-ol amino acids. Preliminary mechanistic studies revealed that major nucleophilic attack of water (S(N)2 type) at high-valent Pd center contributes to the final C-O(H) bond formation.
Iodocyclization of the (tolylsulfonyl)- and (trichloroacetyl)carbamates of secondary .alpha.-allenic alcohols. Highly diastereoselective synthesis of syn-1,2-amino alcohols and trans-5-alkyl-1-oxo-2-oxazolidine-4-carboxylic acids
摘要:
The iodocyclization of tosyl- and (trichloroacetyl)carbamates 9 and 10, respectively, of secondary alpha-allenic alcohols is described. The cyclofunctionalization reactions are highly diastereoselective, providing trans-5-alkyl-4-(1-iodoethylene)-2-oxazolidinones 11 and 12 as the major diastereomers in ratios of 6.3:1 to > 99: < 1. The mechanism of cyclization involves the initial formation of diiodides resulting from the addition of I2 to the terminal olefin of the allene moiety, followed by a kinetically controlled intramolecular SN2' displacement of iodide. Hydrolysis and acetylation of the N-tosyloxazolidinones 11 provide syn-1,2-amino alcohol derivatives 15. Alternatively, ozonolysis of the vinyl iodides derived from the cyclization of the (trichloroacetyl)carbamates 12 provides a novel, efficient, and highly diastereoselective route to trans-5-alkyl-2-oxazolidinone-4-carboxylic acids 25 and esters 26.