Ergosteryl acetate

The type of O2 adduct depends on the donor structure. For example, tetraphenyl-oxirane forms an ozonide (78), " 1,4-bifunctional radical cations form dioxanes (79) conjugated dienes form cyclic adducts (80) and ergosteryl acetate (81) forms the 5a,8fl-peroxide (82) at —78... 

Prominent among the latter substrates is ergosteryl acetate (18) which was converted to the 5a,8a-peroxide (19) by irradiation in the presence of trityl tetrafiuoroborate in methylene chloride at - 78 °C [152], In several cases, oxygenation products have been useful in establishing the structures of unusual radical cations (vide infra). 

In the early 70s, Barton and co-workers reported that irradiation of a mixture of ergosteryl acetate 40 and a new non conventional electron acceptor, i.e., trityltetrafluoroborate (C6H5)3C+BF4, in methylene chloride in the presence of oxygen at — 78° led quantitatively to the corresponding 5a,8a-ergosteryl peroxide 41 [125] ... 

The complexation of chiral dienes leads to the formation of diastereomeric j -diene iron tricarbonyl complexes. An early example was actually carried out for the protection of the diene unit found in the steroid B-ring of ergosteryl acetate (equation 53) neither the stereochemical assignment nor the diastereomer ratio were estabhshed. Similarly, the tricarbonyl iron complex of calciferol was also prepared. ... 

Decomplexation of ArCr CO)3. The chromium carbonyl complexes of arenes are useful for activation of the aryl group to nucleophilic attack (6, 28, 125-126 7, 71-72). Decomplexation has been effected with iodine or by photochemical oxidation with destruction of the expensive Cr(CO)3 unit. A more recent method involves reflux with pyridine to form Py3-Cr(CO)3 in yields of 70-100%. The pyridine complex in the presence of BF3 can be reused for preparation of ArCr(CO)3. Isomerization of 1,3-dienes. Ergosteryl acetate (1) is isomerized by chromium carbonyl to ergosteryl 83 acetate (2) in 81% yield. Under the same conditions ergosteryl 83 acetate (3) is isomerized to ergosteryl 81 acetate (4). 80th reactions involve isomerization of a cisoid diene to a transpid diene. In contrast iron carbonyl isomerizes steroidal transoid 3,5- and 4,6-dienes to 2,4-dienes. ... 

Both benzoylnitroso and benzyloxycarbonylnitroso derivatives undergo addition in a nonre-gioselective manner to ergosteryl acetate. Attack occurs only from the a-facc of the diene moiety giving 2 and 329-30. 

Unlike other classes of C-nitroso compounds, oxidation of A-hydroxy-Af-phenylurea in the presence of ergosteryl acetate leads to only one detectable adduct 11, whose structure was assigned on the basis of 1H NMR33. 

Furthermore, the adduct 1 reacts at 80 °C in benzene with ergosteryl acetate with low regiose-lectivity to give two regioisomers 3 and 4 in a 68 32 ratio. The reaction proceeds, however, with total diastereoselectivity, since the addition occurs exclusively from the a-faee34. 

Reaction of Ergosteryl Acetate with 9,10-(,V-Cyanoepoxyiniino)-9,10-dihydro-9,10-diniethylanthracene to Give Adducts 3 and 434 ... 

A transient nitrosoimine 1, which can be trapped by an appropriate diene, is formed by reaction of an amidooxime and lead tetraacetate. Thus, in the presence of ergosteryl acetate, the corresponding adduct 2 can be obtained with total substrate-induced regio- and stereoselectivity in 65% yield ( HNMR)30 36. 

Another interest in the use of triplet oxygen lies in the oxidation of dienes with photochemical activation (Type 1, above) with formation of endoperoxides as products. The first example of this reaction was observed in the early 1970 s. Thus, reaction of ergosteryl acetate (107) in the presence of trityl tetrafiuoroborate and Lewis acids in the presence of light yielded the endoperoxide 108 (equation 28), With certain Lewis acids this reaction could be thermally, rather than photochemically, activated. Cation radicals were shown to be the intermediate active species, as was borne out by a comparative oxidation of the isomeric lumisteryl acetate which was inactive under these conditions but reacted easily with singlet oxygen . This reaction was later extended to other substrates. Thus, the intermediacy of cation radicals was also indirectly observed by the fact that the r-butyl substituted 1,3-cyclodiene 109 gave a dimeric product 110 (equation 29) via the cation radical intermediate in addition to the usual endoperoxide llOa ,... 

Another synthesis of side-chain-hydroxylated cholesta-5,7-dien-3/S-ol derivatives uses the aldehyde (386), prepared by ozonolysis of the adduct of ergosteryl acetate with 4-phenyl-l,2,4-triazoline-3,5-dione. An aldol condensation between the aldehyde (386) and the pre-formed enolate of 3-methyl-3-tetrahydro-pyranyloxybutan-2-one (387) led to the enone (388), after acidic work-up. Reduc-... 

Isomerization of polyenes. A Pfizer group found that sulfur dioxide in pyridine isomerized ergosteryl acetate (1) into the A - or Bz-isomer (4) probably via the... 

Similar reactions have been reported with various polyenes, but failed with ergosteryl acetate tricarbonyliron and the cyclooctatetraene complex (see, however, results with the use of Simmons-Smith reagent). ... 

The photochemical cycloaddition of 4-methyl-l,2,4-triazoline-3,5-dione to the dibenzo-cyclooctatetraene 289 yields 3.5% of the cycloadduct 290, together with 36% of 291, the product of a di-jr-methane rearrangement (equation 153. Anthrasteroids 293 (R = H, Ac or COPh) are produced in an oxidative rearrangement when the phenyltriazoline-dione adduct of 292 is treated with boron trifluoride etherate. The 5,7-diene system of ergosteryl acetate 294 can be protected by cycloadduct formation, allowing selective hydrogenation of the 22,23-double bond " ... 

Ergosteryl acetate can be converted to its peroxide by triplet oxygen in the presence of a catalytic amount of SbFg or SbClg under illumination (Scheme 14.39) [101]. 

The dipolar cycloaddition of 2-diazopropane to l-methyI-3-phenyl-pyridazin-6-one proceeds at 0°C via an unstable cycloadduct (143), which is thermally decomposed to 144 as the main product, together with 145 and 146. " A cycloadduct is also formed between ergosteryl acetate and the diazaquinone formed from maleic hydrazide. ... 

Ergosteryl acetate tricarbonyliron can be obtained in y-lTTfo yield by use of this reagent. Use of dodecacarbonyUron gives the complex in low yield. The tricarbonyliron complex is useful for protection of the diene system during reactions of the isolated double bond. ... 

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