0000000000132969
AUTHOR
Maria Eugenia González-rosende
Stereoselective Synthesis of trans-4,5-Disubstituted Oxazolidin-2-ones by Intramolecular Conjugate Addition of N-p-Toluenesulfonyl Carbamates.
p-Toluenesulfonyl carbamates (2a-d) were prepared starting from allylic alcohols (3), in which the double bond is conjugated with an electron withdrawing group. In the presence of a catalytic amount of DBU, an intramolecular cyclisation occurred, leading to trans-4,5-disubstituted oxazolidin-2-ones (1a-d) with total stereoselection, which can be precursors of syn-4-hydroxy-3-amino acids.
Unprecedented intermolecular transamidation reaction of N-carbamoylmethyl-N'-tosylguanidines.
[reaction: see text] N-Carbamoylmethyl-N'-tosyl guanidine 2 reacts easily with primary alkylamines to afford substituted carboxamides 3. The reaction proceeds via a five-membered-ring intermediate 5, which could be isolated, and features a rare example of an intermolecular transamidation reaction under mild conditions.
1,3-Oxazin-2-ones vs tetrahydrofurans by iodocyclisation of 2-alkoxycarbonylamino-3-alken-1-ols
Abstract Iodocyclisation of primary homoallylic alcohols 2a – d , containing either a 2- t -butoxy- or a benzyloxycarbonylamino group, was studied, in order to establish the nucleophilic group involved in cyclofunctionalisation. In fact, the N - t -Boc derivative 2a gave the oxazinone 3 , exclusively, whereas starting from the N -Cbz derivative 2b a diastereomeric mixture of substituted tetrahydrofurans 4 and 5 resulted in ratios depending upon the reaction conditions. These results were rationalised by means of computational methods. On the contrary, migration of both the t -butyl or benzyl group to the hydroxy group was observed when both 2c and 2d underwent cyclisation to give the corres…
Homochiral oxazolidin-2-ones and imidazolidin-2-ones by tandem nucleophilic addition–conjugate addition
Abstract Treatment of both primary alcohols 1a , b and secondary amines 1c , d , tethered to a Michael acceptor with ( R )-phenylethyl isocyanate in the presence of DBU gave in good yield and high stereoselection diastereomeric mixtures of oxazolidin-2-ones 2a , b and 3a , b and imidazolidin-2-ones 2c , d and 3c , d , respectively. The cyclisation reaction was studied computationally by ab initio quantum mechanical methods. The observed stereoselectivity was explained on the basis of the different stability of both anions and transition states leading to 2a and 3a , respectively. The usefulness of the method was proven by conversion of 2a into the enantiomerically pure bioactive amino acid …