Stannylcupration of chiral γ-amino acetylenic esters: Stereocontrolled synthesis of 3-tributylstannyl γ-amino (E)-alkenoates a as precursors of 4-stannylated pyrrolinones

Stereoselective Synthesis of Polysubstituted Piperazines and Oxopiperazines. Useful Building Blocks in Medicinal Chemistry

“…Our research group has been for long time interested in the use of amino acids as building blocks for organic synthesis, and following this approach we have been able to develop new synthetic methodologies to prepare biologically active chiral heterocycles. [64][65][66][67] Taking advantage of such experience we have been also interested to design an efficient and scalable route to enantiomerically enriched 2oxopiperazines, and piperazines. In our approach the substitution and the stereochemistry at the substituted carbon atom could be dictated by the choice of the starting amino acid and the two nitrogens of the ring can be orthogonally protected, as this would allow the stepwise arrangement of substituents, should the heterocyclic ring be used as a molecular scaffold.…”

Silylcupration of (R)-2,2-Dimethyl-3-(tert-butoxycarbonyl)-4-ethynyloxazolidine: A Stereoselective Approach to the Synthesis of γ-Silylated Saturated and Unsaturated α-Amino Acids

“…The oxazolidine moiety is widely employed as a synthetic equivalent 1 of α-amino acids, and the presence of an unsaturated lateral chain ,,, has been exploited to obtain precursors to ethynyl- and vinylglycine derivatives. For example, addition of 1 to 2 , afforded, regio- and stereoselectively, the corresponding γ-stannylated ( E )-ethenyloxazolidine 3 , a useful intermediate which was subsequently coupled with electrophiles under Pd catalysis to give the corresponding γ-substituted amino acids precursors 4 (Scheme ). One of the most remarkable features of this protocol is that the resulting compounds showed no loss of stereochemical information, confirming metallocuprates as suitable reagents to be used on enantiomerically enriched compounds. , …”

Asymmetric Total Synthesis of (+)‐Bermudenynol, a C15Laurencia Metabolite with a Vinyl Chloride Containing Oxocene Skeleton, through Intramolecular Amide Enolate Alkylation

“…We further envisaged that the requisite (E)-g-chloro allylic bromide moiety in IAEA substrate 4 could be elaborated from the terminal alkene functionality in known C(12)/C(13)-syn diol derivative 5, which was accessed in four steps from 6 by Evans alkylation and chelation-controlled nucleophilic addition. [11] Chemoselective reduction of the ester in 11 in the presence of a-alkoxy dimethylamide by treatment with the ate complex generated from DIBAL-H and nBuLi [12a] (À78 8C, then NaBH 4 /EtOH, À78 8C to RT), and subsequent tin-chlorine exchange [13] led to the desired (E)-g-chloro allylic alcohol 13 (55 % yield for the two steps). The terminal alkene functionality in 7 was used to install the (E)-g-chloro allylic bromide moiety required in key IAEA substrate 4 as follows: one-pot cleavage of alkene 7 by a modified Lemieux-Johnson oxidation, [8] followed by Ohira-Bestmann alkynylation [9] of the resultant aldehyde 8, gave the desired alkyne 9 in good overall yield (78 % yield for 3 steps from 5).…”

“…Regio-and stereoselective hydrostannylation of propargylic ester 10, prepared by palladium-catalyzed oxidative carbonylation of alkyne 9, [10] was accomplished under the stannylcupration conditions described by Pancrazi and co-workers to afford the desired (E)-vinyl stannane 11 (53 % for the two steps). [11] Chemoselective reduction of the ester in 11 in the presence of a-alkoxy dimethylamide by treatment with the ate complex generated from DIBAL-H and nBuLi [12a] (À78 8C, then NaBH 4 /EtOH, À78 8C to RT), and subsequent tin-chlorine exchange [13] led to the desired (E)-g-chloro allylic alcohol 13 (55 % yield for the two steps). This same ate complex is used elsewhere to reduce an aalkoxy dimethylamide group to the corresponding aldehyde at 0 8C to room temperature (see below), so the temperature effect makes the chemoselectivity here highly tunable.…”