L selectride

L-Selectride or Super Hydride, 67°, 88-92% yield. Other methods for converting thebaine to oripavine have not been successful. ... 

Cryogenic conditions (-78 °C) and an expensive reagent (L-Selectride ) to obtain high selectivity for carbonyl reduction in 5 Additional cost for cryogenic step... 

Incompatibility of the nitrile group with the oxidative work-up of the L-Selectride reduction using basic hydrogen peroxide Significant hydrolysis to the primary amide with concomitant exothermic activity and loss of product... 

After salt break chiral acid 11 was converted to the methyl ketone 13 in essentially quantitative yield via the intermediacy of the Weinreb amide and processed as an oil without further purification (Scheme 9.6). The carbonyl group in 13 was then reduced to the secondary alcohol 16 using L-Selectride as previously described in 97% assay yield. We were pleased to find that an attainable reaction temperature of-50°C was sufficient to obtain high selectivity of >98 2, and that, in the absence of the reactive nitrile group, no issues were observed or during... 

L-Selectride remains the reagent of choice, but an attainable temperature of... 

Benzyl-nitrogen, sulfur, or -oxygen bonds are somewhat susceptible to hydrogenolysis, either during catalytic hydrogenation (30, 31), or upon treatment with L-selectride (32), or even lithium aluminium hydride (33). 

The first asymmetric synthesis of (-l-)-abresoline was achieved from the chiral piperidine derivative 153, which upon treatment of its hydroxy side-chain substituent with carbon tetrabromide, triphenylphosphine, and triethyl-amine cyclized to the frarcr-quinazolidine 154. Deketalization and silyl protection of the phenolic group, followed by stereoselective reduction with lithium tri-t -butylborohydride (L-Selectride ), gave an alcohol, which after acylation and deprotection furnished (-l-)-abresoline 155 (Scheme 25) <2005TL2669>. 

Although a major drawback to this reaction was the destruction of the C3 stereochemistry, it represented the first successful attempt to open the peroxide in a productive manner. To regain the C3 stereocenter, we treated vinylogous ester 48 (from acid-promoted solvolysis of 49b) NaBH4 but only to find alcohols were isolated in a 4 1 ratio (Scheme 8.12). Fortunately, L-Selectride gave exclusively... 

We first examined ketone 48 and hydroxy ketone 56 because (1) no reduction of C5a-carbonyl in 48 occurred when using L-Selectride to reduce the C3-ketone and (2) NaBH4 did not touch the C5a-carbonyl group in hydroxy ketone 56. By using minimized Spartan model of vinylogous ester 48 and the X-ray structure of hydroxy ketone 56, we found unique conformational elements (Fig. 8.10) in addition to fully validating the aforementioned NMR analysis of possible positions for H8a when C8a is ip2-hybridzied and H7 when C8a is sp3-hybridized. In 48,... 

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