Osmylation Of diene

The diastereoselective synthesis of higher sugars was accomplished by bZi-osmylation of sugar derived dienes using OsO4-NMO4°. As shown in equation 23, osmylation of diene 26 afforded diastereomeric sugars 27, 28, and 29 in 90% overall yield in a 6.6 1.2 1.0 ratio, respectively. 

A stereoselective osmylation approach was applied to the synthesis of C(l)—C(7) and C(7)—C(13) subunits of erythronolide A41. A key synthon of the erythronolide A seco acid, 30, was prepared in an enantiomerically pure form by utilizing a stereoselective osmylation of the chiral hydroxy (Z, )-diene ester 31 and subsequent hydrogenation of the resulting butenolide 32 (equation 24). 

Regio- and stereoselective dihydroxylation of dienes functionalized at the allylic position with a benzene sulfone group has been reported42. Osmylation of dienic sulfones 33, a potential key synthon for forskolin, occurred exclusively on the A6-7 double bound and preferentially from the a-face of the traws-fused bicyclic molecule, presumably due to a combination of steric and electronic factors (equation 25). While the reaction of diene sulfones proceeded sluggishly under catalytic conditions, treatment of 33a with a stoichiometric amount of OSO4 resulted in quantitative yield of diastereomeric diols 34a and 35 in a 9 1 ratio, respectively. Protecting the hydroxy group of the dienol as its t-butyldimethylsilyl ether (33b) affords diol 34b exclusively. 

Substituted 4,5-dihydro-5-vinylisoxazoles (40), obtained by regio- and stereospecific cycloaddition of nitrile oxides to dienes, undergo smooth osmium-catalyzed c/s-hydro-xylation to give amino-polyol precursors (equation 28)45. The reaction is anti selective, the diastereomeric ratios ranging from 73 27 up to 99 1. Highest stereoselectivities were observed when R3 was methyl. Thus, whereas osmylation of 40a afforded a 78 22 mixture of 41a and 42a, respectively, in 80% overall yield, similar treatment of 40b resulted in a 92 8 mixture of 41b and 42b, respectively, in 70% overall yield. The cycloaddition-osmylation sequence allows control of the relative configuration of up to 4 contiguous asymmetric centers. 

Osmylation of C—C double bonds adjacent to the (diene)Fe(CO)3 functionality has been reported (Scheme 57)205. This methodology has been used in the enantiospecific synthesis of 5,6- and 11,12-diHETEs. 

Cyclopentadiene undergoes catalytic osmylation to produce the bis(cyclic) boronate in good yield and with excellent selectivity for the a -product (Equation 61) <1998JOC7322>. The reaction was found to be effective for a range of dienes (see also Sections 10.21.9.3.4(iii)(b) and 10.21.9.4.4). 

The elegant pinacol rearrangement of 1 to 2, mediated by ( ) 1 3, exposed a ketone that might usually need to be protected. In this case, however, the ketone is so buried in the inside-outside ingenol skeleton that it is unreactive. After several further manipulations, a spectacular osmylation of the diene 12 led to ingenol 3, in an overall 45-step sequence. 

Isolated double bonds can be oxidatively cleaved in systems containing a conjugated diene moiety if it is protected as a tricarbonyl(diene)iron complex44. Dienal 39 was acquired in 49% yield by a two-step osmylation-periodate cleavage sequence (equation 27). In contrast, ozonolysis of the polyene complexes is reported to lead to destruction of the complex. 

The original synthetic plan contemplated the use of the diene of the type A (Scheme 14) as the pivotal intermediate for pancratistatin by selective modification of one of the double bonds. However, the propensity of the benzylether 101 to undergo facile aromatisation to the diphenylcarboxylic acid 102, necessitated hydroxylation of the olefin 101 prior to base-induced elimination of elements of hydroiodic acid. The cis-diol 103, thus secured, was converted via the olefin 104 into tavu-a-bromoacetate 105 in an unusual reaction studied by Moffat [28], involving the use of 2-acetoxyisobutyrylbromide. The new diol 106 secured from 105 by osmylation protocol was converted into the corresponding stannylene 107 that on successive... 

Oxo ester complexes with nitrogenous bases (L). Although most of these species contain the osmyl unit there are so many of them that it is appropriate to deal with them in a separate reaction. Most of the complexes have an Os L ratio of 1 2 (the majority taking the form 0s02(02R)py2) and so we consider such species first and include those complexes of the type 0s02(02R)(L—L), where L —L is a bidentate N donor (usually 2,2 -bipyridyl). Within this first section we consider first the species derived from alkenes R or diols R(OH)2, viz. 0s02(02R)L2 or 0s02(02R)L—L, and then species derived from dienes, trienes and alkynes. We then deal with the much smaller body of complexes where the Os L ratio is 1 1. 

The C-glycoside 178 was used by Boyd and Sulikowski [87] in the total synthesis of enantiomerically pure urdamycinone B (182) and 104-2 (183) making use of the diene 107 derived from shikimic acid (Scheme 29) and the NMO oxidation to generate the C-5 phenols (Scheme 40). Thus, the bromonaphthoquinone 179 (prepared by treatment of phenol 178 with NBS) formed the tetracycle 180 through a Diels-Alder reaction with the diene 107 in analogy to sugar-free reactants. Osmylation to a cis-diol, deprotection, oxidation, and acetalization gave the acetonide 181. The decisive step in the aromatization to 182 and 183 was the reaction with NMO (Scheme 46). Aromatization was also effected by direct periodane oxidation of adduct 180 to derive 182 after deprotection. 

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