Imide, reduction

In an effort to identify a more stereoselective route to dihydroagarofuran (15), trimethylsilylated alkyne 17 was utilized as a substrate for radical cyclization (Scheme 2). Treatment of 17 with a catalytic amount of AIBN and tri-n-butyltin hydride (1.25 equiv) furnishes a mixture of stereoisomeric vinyl silanes 18 (72% combined yield) along with an uncyclized reduction product (13% yield). The production of stereoisomeric vinyl silanes in this cyclization is inconsequential because both are converted to the same alkene 19 upon protodesiiyiation. Finally, a diastereoselective di-imide reduction of the double bond in 19 furnishes dihydroagaro-... 

In 2007, Jacobsen and co-workers reported the enantioselective Pictet-Spengler-type cyclization of P-indolyl ethyl hydroxylactams affording highly enantioenriched indolizidinones and quinolizidinones with fully substituted stereogenic centers [205]. The hydroxylactam substrates prepared either by imide reduction using... 

Two new syntheses of racemic mesembrine have been described. In the first, outlined in Scheme 1, an improved synthesis of the penultimate 2-pyrroline (8) was achieved annelation of this afforded ( )-mesembrine (9). The second (Scheme 2) incorporates a regioselective borohydride imide reduction. Investigations on the biosynthesis of mesembrine alkaloids have revealed that a stereospecific protonation occurs at C-7 [see formula (9)] as one of the late stages. ... 

See Problem 16.47 for the acidity of imides. Reduction of N-Containing Compounds 1. Nitro Compounds... 

Cyclic imide reduction. The reagent reduces imides to give hydroxy lactams in a regioselective manner, which is different from LiBHEtj. The complementary is very useful in synthesis. 

Whitlock et al. developed a new method to synthesize bacteriochlorins and isobacteriochlorins selectively it involved diimide reduction of porphyrins. 2 Di-imide reduction of metal-free tetraphenyl-chlorin H2(TPC) afforded tetraphenyl-bacteriochlorin H2(TPBC) 140 in 84% yield, while reduction of zinc tetraphenyl-chlorin Zn(Xrc) produced the Zn(II) complex of tetraphenyl-isobacteriochlorin 141 in 57% yield (Scheme 40). 

Miller et al. used various ohgoimides in conjunction with several generations of poly(benzylether) dendrons to synthesize molecular dumbells", the largest of which extended 9.6 nm in length. The electrochemistry of the imide reduction was studied using cyclic voltammetry at scan rates up to 100 Vs , and it was found that the dendrimer did not... 

Di-imide reduction is also a useful method for quantitative hydrogenation of unsaturated ADMET polymers [48]. This is a general method that has been used to hydrogenate both ADMET and ROMP polymers. 

The imides, primaiy and secondary nitro compounds, oximes and sulphon amides of Solubility Group III are weakly acidic nitrogen compounds they cannot be titrated satisfactorily with a standard alkaU nor do they exhibit the reactions characteristic of phenols. The neutral nitrogen compounds of Solubility Group VII include tertiary nitro compounds amides (simple and substituted) derivatives of aldehydes and ketones (hydrazones, semlcarb-azones, ete.) nitriles nitroso, azo, hydrazo and other Intermediate reduction products of aromatic nitro compounds. All the above nitrogen compounds, and also the sulphonamides of Solubility Group VII, respond, with few exceptions, to the same classification reactions (reduction and hydrolysis) and hence will be considered together. 

Industrial Synthetic Improvements. One significant modification of the Stembach process is the result of work by Sumitomo chemists in 1975, in which the optical resolution—reduction sequence is replaced with a more efficient asymmetric conversion of the meso-cyc. 02Lcid (13) to the optically pure i7-lactone (17) (Fig. 3) (25). The cycloacid is reacted with the optically active dihydroxyamine [2964-48-9] (23) to quantitatively yield the chiral imide [85317-83-5] (24). Diastereoselective reduction of the pro-R-carbonyl using sodium borohydride affords the optically pure hydroxyamide [85317-84-6] (25) after recrystaUization. Acid hydrolysis of the amide then yields the desired i7-lactone (17). A similar approach uses chiral alcohols to form diastereomic half-esters stereoselectivity. These are reduced and direedy converted to i7-lactone (26). In both approaches, the desired diastereomeric half-amide or half-ester is formed in excess, thus avoiding the cosdy resolution step required in the Stembach synthesis. 

Hofmann rearrangement, 933 imide (-CONHCO—), 929 primary amine (RNH2), 916 quaternary ammonium salt, 917 reductive amination, 930 Sandmeyer reaction, 942 secondary amine (R2NH), 917 tertiary amine (R3N), 917... 

It was anticipated that two of the three stereochemical relationships required for intermediate 12 could be created through reaction of the boron enolate derived from imide 21 with a-(benzyloxy)ace-taldehyde 24. After conversion of the syn aldol adduct into enone 23, a substrate-stereocontrolled 1,2-reduction of the C-5 ketone car-... 

The partial reduction of cyclic imides is a simple and very useful method for the synthesis of cyclic N-(I-hydroxyalkyl)amides27 or carbamates28. 

Inherent in the reduction of asymmetrically substituted cyclic imides is the problem of regiose-lectivity. Imides, in which one carbonyl group is part of a (thio)carbamate or urea function, usually show complete chemoselectivity for reduction of the other carbonyl group, indicated with an arrow. 

More symmetrical imides may still be regioselectively reduced. In the case of geminally disub-stituted succinimidcs the stcrically more hindered carbonyl function is preferentially reduced with sodium borohydride. The regioselectivity ranges from 79 21 for the dimethyl derivative to > 95 5 for the diphenyl derivative29. For monosubstituted succinimides the selectivity of the reduction is low29, unless the substituent is an acetoxy group35-36. 

Diisobutylaluminum hydride (DIBAL-H) can also be used for partial reduction of cyclic imides37. Although less convenient than sodium borohydride, an important synthetic aspect is the fact that in the reduction of asymmetrically substituted imides, diisobutylaluminum hydride and sodium borohydride may show opposite regioselectivity38,39. 

Some other typical examples of regiosclcctivc reductions of imides with sodium borohydride in ethanol are42 ... 

The synthesis of precursors for the generation of the enantiomerically pure mono- and trans-dioxygenated /V-acyliminium ions of type 335,36 and 643 is achieved by reduction of the corresponding optically active imides. 

In another approach to the meso problem , utilization of a chiral auxiliary attached at nitrogen appears to induce very high stereoselectivity. Reduction of the optically active imide 10a (see Appendix) with tetramethylammonium triacetoxyborohydridc in acetone/ acetic acid at 25 "C gives a 4 96 mixture of the diastcreomers 11a and 12a in 87% yield44. On changing the solvent to acetonitrile/acetic acid the diastereomeric ratio is improved to < 1 99, but the yield is lower (63%). 

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