Amino stannane

An alternative synthesis of nonracemic a-amino stannanes is outlined in equation 3777. The diastereomeric stannanes, obtained by sequential lithiation and stannylation of the starting nonracemic piperidinooxazoline, can be separated by chromatography. Subsequent removal of the chiral auxiliary and N-methylation completes the synthesis. 

Related pyrrolidines 149 and 150 are produced from organolithium species which readily undergo cyclization onto suitably positioned alkenes <20030BC2111>. The amino-stannane starting material undergoes tin-lithium exchange at low temperatures followed by cyclization on warming to produce two stereoisomers in a 4 1 ratio (Equation 51). The major product formed was found to be the stereoisomer 149, contrary to expectation from model studies. 

Fischer carbenes react with silanes and stannanes to form aUcoxy- or amino-stannanes and -silanes. For example,... 

Without additional reagents Acetylene- from amino-stannanes s. 31,490... 

N-Ethylaminotrimethylsilane allowed to react with Irimethyltin bromide, and the resulting complex heated with distillation of the product -> N-ethylamino-trimethyltin. Y 72%.—Tert. organotin amines had to be prepared by another method because of the increased thermal stability of the intermediate complex. E. W. Abel, D. Brady, and B. R. Lerwill, Chem. Ind. 1962, 1333 (ferf-amino)-stannanes from aminomagnesium halides cf. K. Sisido and S. Kozima, J. Org. Chem. 27, 4051 (1962). 

Allyl carbamates also can serve as amino-protecting groups. The allyloxy group is removed by Pd-catalyzed reduction or nucleophilic substitution. These reactions involve formation of the carbamic acid by oxidative addition to the palladium. The allyl-palladium species is reductively cleaved by stannanes,221 phenylsilane,222 formic acid,223 and NaBH4,224 which convert the allyl group to propene. Reagents... 

To enhance the efficiency of the cyanide addition, these workers subsequently reported a three-component asymmetric synthesis of amino nitriles that avoids the use of the previously mentioned undesirable stannane [74], Thus, as illustrated in Scheme 6.23, treatment of the requisite aniline and aldehyde with HCN (toxic but cheap and suitable for industrial use) at —45°C in the presence of 2.5 mol% 65 leads to the formation of 67 with 86 % ee and in 80 % yield. As was mentioned above in the context of catalytic asymmetric three-component alkylations of imines (see Scheme 6.18), the in situ procedure is particularly useful for the less stable aliphatic substrates (cf. 71—73, Scheme 6.23). The introduction of the o-Me group on the aniline is reported to lead to higher levels of asymmetric induction, perhaps because with the sterically less demanding aliphatic systems, the imine can exist as a mixture of interconverting cis and trans isomers. 

Scheme 18 Synthesis of a-amino acid derivatives use of chiral stannane...

The electrophile for the cyclization reaction of an a-amino-organolithium compound is not restricted to a terminal (or phenylthio-substituted) ahcene and examples have been reported using carboxylic amides, alkynes and allyhc ethers." " For example, Fautens and Kumanovic reported that treatment of the bicyclic stannane shown in Scheme 24... 

As indicated in Section ni.B, deprotonation of a carbamate affords a dipole-stabilized a-amino-organolithium that can be transmetalated with copper salts to form cuprates, thereby expanding the versatility of the organolithium. Suitable electrophiles include enones, alkenyl, alkynyl, allenyl and dienyl carboxylic acid derivatives, nitriles and sulfoxides. Dieter and coworkers have shown that the same process can be accomplished via transmetalation of a stannane (Scheme 36). The procedure is particularly... 

Substituted 6-iodopyridazines were the first representatives studied <1995JOC748>. Interestingly, a free amino group is well tolerated and a comparison of Stille reactions on 6-iodo- 170 and 6-chloropyridazin-3-amine 171 with aryl(tributyl)stannanes remarkably revealed that the latter react substantially faster (Equation 28 and Table 7) <2000T1777>. 

The formation of rings with more than seven atoms has unfavorable rates because the addition step is often too slow to allow it to compete successfully with other pathways open to the radical intermediate. In stannane based chemistry for example, premature hydrogen abstraction from the organotin hydride is difficult to avoid. However, Baylis-Hillman adducts 111 derived from enantiopure 1-alkenyl (or alkynyl)-4-azetidinone-2-carbaldehydes are used for the stereoselective and divergent preparation of highly functionalized bicycles 112 and 113 fused to medium-sized heterocycles (Scheme 38) [80, 81]. The Baylis-Hillman reaction using nonracemic protected a-amino aldehydes has been attempted with limited success due to partial racemization of the chiral aldehyde by DABCO after... 

Crossley and his associates described new synthetic routes to a-amino acids and y-oxygenated a-amino acids through Bu3SnH-mediated denitration chemistry (equation 50)287. Ikeda and his associates reported the stannane-mediated removal... 

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