Tributyltin hydrides, reduction

The 8-methyl-8,14-cycloberbine 364, derived from the protoberberine 324 via the betaine 363, was reduced with sodium borohydride or lithium aluminum tri-tert-butoxyhydride to give a diastereoisomeric mixture of cis-and trans-alcohols (7.8 1 or 1 7.8, respectively) (Scheme 64).t)n exposure to formaldehyde the mixture underwent N-hydroxymethylation and subsequent intramolecular substitution on the aziridine ring to give the oxazolidine 365. Removal of the hydroxyl group in 365 was accomplished by chlorination followed by hydrogenolysis with tributyltin hydride. Reductive opening of the oxazolidine 366 with sodium cyanoborohydride afforded ( )-raddeanamine (360), which has already been converted to ochotensimine (282) by dehydration. 

Tributyltin hydride reduction of carbonyl compounds. The reduction of carbonyl compounds with metal hydrides can also proceed via an electron-transfer activation in analogy to the metal hydride insertion into TCNE.188 Such a notion is further supported by the following observations (a) the reaction rates are enhanced by light as well as heat 189 (b) the rate of the reduction depends strongly on the reduction potentials of ketones. For example, trifluoroacetophenone ( re<1 = —1.38 V versus SCE) is quantitatively reduced by Bu3SnH in propionitrile within 5 min, whereas the reduction of cyclohexanone (Erea — 2.4 V versus SCE) to cyclohexanol (under identical... 

The reaction of alkyl dihalogenoacetate magnesium enolates with 2,3-isopropylidene-D-glyceraldehyde affords the expected /3-hydroxy-a-dihalogenoesters . The erythro isomer is obtained with isopropyl dichloroacetate magnesium enolate. This result is in agreement with theoretical models. 2-Deoxy-pentono-1,4-lactones are obtained after removal of the halogen atom by either Raney nickel or tributyltin hydride reduction (equation 89). 

The tributyltin hydride reduction of dihaloaziridines, e.g. (266), represents another example where the ring system has been maintained (79CJC1958). Especially noteworthy is the retained configuration associated with the reaction. This behavior differs from the cyclopropyl analog and was explained on the basis of increased s-character in the exocyclic bond caused by the nitrogen atom. 

The tributyltin hydride reduction usually proceeds without complications. The most common byproduct is starting alcohol, which is postulated to be derived from a mixed thioacetal. Use of the phenyl thionocarbonate ester has been reported to minimize this side reaction in cases where it is a problem.6... 

The iodocyclization of 4-methyl-5-hexenoic acid performed under conditions of thermodynamic control (iodine in acetonitrile in the absence of a base) leads to the preferential formation of the /raw.v-diequatorial 5-lactones (94 6) in 77% yield1. Similar results were observed starting from (S)-4-methyl-5-hexenoic acid (1), obtained from citronellol, with iodine in acetonitrile, followed by tributyltin hydride reduction. The 5,6-dimethylvalerolactone 2 was obtained in 40%) yield and 93.5 6.5 (irans/cis) diastereoselcctivity 2. 

Organotin hydride reductions of a variety of polycyclic halides containing three-membered rings have been studied, including the stereoselectivity in the triphenyltin hydride reduction of 6jS-chloro-3,5-cyclocholestanes, Tributyltin hydride reduction of both syn- and anti-1-chloro-2-methylnortricyclene (35) afforded cn fo-5-methylnorbornene (36) as the major product, with very little of the e.w-isomer. ... 

Ring cleavage was extremely rapid in the tributyltin hydride reduction of 9-bromotricyclo-[3.3.1.0 ]nona-3,6-diene (9-bromobarbaralane, 43) excellent yields of bicyclo[3.2.2]nona-2,6,8-triene (44) were isolated, mixed with only a trace of the unrearranged barbaralane. ... 

A variation of the tributyltin hydride reduction is available that can be applied to alcohols. The alcohol is converted to a thionocarbonate and then reduced with BusSnH and AIBN, which circumvents the need for... 

Completion of the formal synthesis of ( + ) carpetimycin A 48 was effected by tributyltin hydride reduction of the bromohydrin 43, to give predominantly the required cis a-hydroxyalkyl P-lactam 46 in 63% yield, together with the... 

Osmylation of the chirally masked 2-alkoxypent-3-enal 1 and subsequent functional group manipulations furnished enantiopure 5-deoxy-L-lyxose and -xylose derivatives. A new preparation of 5-deoxyribonolactone derivative 2 from ribonolactone by tributyltin hydride reduction of a 5-chloro-5-deoxy intermediate has been published. Conversion of compound 2 to a 5 -deoxy-nucleoside analogue is covered in Chapter 20. A multistep synthesis of methyl 5-0-benzoyl-2,3-dideoxy-P-D-g/ycero-pentofuranose (4) from D-xylose involving Raney nickel desulfurization of compound 3 (see Chapter 11) has been described. Several deoxy-ketoses have been prepared by Raney nickel desulfurization of 1-thio-ketose derivatives obtained by enzyme-catalysed aldol condensations (see Vol. 29, Chapter 2, Scheme 1). An example is given in Scheme 1. ... 

Along the same means, the tributyltin hydride reduction of thioesters and sele-noesters to aldehydes with palladium catalysis was reported (Scheme 27). A detailed discussion of the mechanism was presented. 

A full paper on the use of the palladium-catalysed tributyltin hydride reduction of acyl chlorides to aldehydes has appeared. The importance of the palladium species in these reactions is clearly seen during the reduction of the acid chloride (1), which gives citronellal in the presence of catalyst, but yields menthone in its absence (Scheme 3). 

Hydrolysis in buffered solution of the bromomethylenecyclopropanes (275) leads almost exclusively to allenic tertiary alcohols (276). This constitutes a homologation sequence for allenes since the monobromo-compounds are accessible by tributyltin hydride reduction of the dibromo-analogues which are themselves obtained by dibromocarbene addition to allenes. Cyclonona-1,2-diene (277) having high optical purity has been prepared by... 

Another type of reactivity was disclosed for difluorochloro group in pyrimidine series. Recently Iaroshenko, Langer and co-workers shown that difluorochloro substituted pyrimidines 1227 can be converted into corresponding difluoromethyl pyrimidines 1228 by radical reduction with tributyltin hydride in the presence of AIBN in moderate yields. In addition, CFaCl-substituted pyrimidines 1227 were transformed to the corresponding l,l-difluorobut-3-enyl pyrimidines 1129 by reaction with aUyltributyltin and AIBN. In this case the yields of transformation are lower in comparison with tributyltin hydride reduction (Schane 269) [412]. 

Most functional group conversions abxmdantly used on carbohydrate derivatives are also compatible with thioglycosides, e.g. SN2-displacements of sulfonates [37], azo transfer [38], and deoxygenation by tributyltin hydride reduction of o-carbonyl carbamates [39]. During oxidations care has to be taken so not to obtain the sulfoxide derivative (if that is not desired). DMSO and also PDC-mediated oxidations can usually be performed without problems [40]. 

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