Steroids and Related Natural Products. VIII. Synthesis of Oxasteroids<sup>1,2</sup>

Pettit, George R.; Kasturi, T. R.

doi:10.1021/jo01069a087

Cited by 41 publications

(9 citation statements)

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“…For our purposes a direct reductive route (12 -t 13) was certainly more attractive, and to this end we investigated the utilization of the sodium borohydride -boron trifluoride combination which had been developed by Petitt and co-workers (23)(24)(25)(26). This reagent has been shown (23,24) to effectively reduce aliphatic eSters and lactones to the corresponding ethers; however, when either the alcohol or acid moiety was aromatic, ethers were not formed and only the corresponding alcohols were obtained (25,26).…”

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“…This reagent has been shown (23,24) to effectively reduce aliphatic eSters and lactones to the corresponding ethers; however, when either the alcohol or acid moiety was aromatic, ethers were not formed and only the corresponding alcohols were obtained (25,26). Nevertheless, we have applied this technique to the reduction of the 2'-hydroxybiphenyl-2-carboxylic acid lactones (12a-d) and have obtained only the corresponding.…”

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6H-Dibenzo[b,d]pyrans. I. Synthesis

Devlin¹

1975

Can. J. Chem.

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The preparation of 2′,4′-dihydroxy- and 2′,6′-dihydroxybiphenyl-2-carboxylic acid lactones (3 and 4) is described. Grignard addition to or direct boron trifluoride etherate – sodium borohydride reduction of these lactones yields respectively these 6,6-substituted (e.g. 6) or the 6,6-unsubstituted (13a) 6H-dibenzo[b,d]pyrans. Evidence that the reductive route proceeds without ring cleavage is presented.

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6H-Dibenzo[b,d]pyrans. I. Synthesis

Devlin¹

1975

Can. J. Chem.

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“…\I7e had also used persulfuric acid to oxidize nortestosterone to the hydroxylacto~le IV ( X = OH) in lo\\; yield (27). This reaction would be expected, on the basis of Pettit's lnechanisl~i (13) and of the known stereospecificity of the Raeyer-Villiger reaction (29), to yield a 5a-lactone, and hence may be construed as further evidence for the configurations shown in Reaction Scheme 1. Can.…”

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confidence: 82%

STEREOCHEMICAL STUDIES: VI. REACTIONS OF 3β-Hydroxy-4-Oxa-5α-Estrane AND 3α,17β-Dihydroxy-4-Oxa-5α-Estrane

Edward¹,

Ferland²

1966

Can. J. Chem.

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'The configurations a t the 3 positions of 3D-hydrosy-4-oxn-5or-cstrane and of 3a,17@-dihydrosy-4-oxa-5a-estrane were assigned frorn a study of the anomerizatior~s of these compounds in aqueous tetrahydrofuran. 3a-Chloro-4-oxa-5a-estrane solvolyzed in alkalirie rnethanol to give a mixture of 3a-and 3D-methoxy-4-oxa-5a-estrane, the former predominating. 'The differer~ce in the solvolytic behavior of 3a-chloro-4-osa-cia-steroids arid of a-glycosyl halides is discussed.T h e solvolysis of 3cr-cl~loro-4-oxa-5~-cholesta1~e in buffered or alltaline alcohols gives 3-allcosy derivatives 116th predoininant retention of configuration (1). The solvolysis of acylglycosyl halides, on the contrary, generally gives a product of inverted config~~ration (2) if participation by neighboring groups is avoided (3, 4) and if there is not excessive hindrance t o approach of the substituting molecule (5). A possible explanation for the behavior of the steroidal chloroether \\las considered t o be the shielding of the 0 face of ring X by the angular methyl group (I). Although the shielding of this ring is believed t o be less complete than the shielding of rings C and D (6), it has been invoked frequently to explain cases of preferential reaction of ring A on its a face; a recent exanlple is the h ydroboration of A'-, A2-, A3-, and A4-cl~olestenes (7).T o test this possibility, n-e have synthesized a cl~loroether ( I X , X = I-I) laclting the angular methyl group, and have studied the stereochenlistry of its solvolysis in methanol. Synthetic RoutesThe synthetic route t o the desired cl~loroether I X (X = I-I) is outlined in Reaction Sche~ne 1. T h e three-stage preparation from estrone of the unsaturated ltetone I (X = I-I) is described in the literature (8). Ozonolysis of this ltetone gave the lceto acid I1 ( X = I-I), \vhich \\-as reduced \vith sodium borohydride t o the hydroxy acid I11 ( X = I-I, Y = OH). On acidification, the latter fornled the lactone IV (X = I-I). T h e a configuration a t the 5 position of the lactone \lras indicated by its nuclear magnetic resonance (n.m.r.) spectrunl (discusscd in ref . 9), and by the negative shift in molecular rotation (Table I) when it was hydrolyzed in allcaline solution (10, 11). I-Iydrogenation of the lactone over platinuill in acetic acid containing a small amount of perchloric acid gave the ether V (X = I-I), whereas reduction with lithium alu~niniunl hydride (cf. refs. 1 and 12) or diborane (cf. Dehydration of the heiniacetal with phosphorus oxychloride in pyridine yielded the dihydropyran VIII ( X = I-I), which in ether solution added hydrogen chloride (cf. refs. 1 and 14) to give the reactive chloroether I X ( X = I-I). This reaction is ltnolvn t o be reversible (1,15), and the sanlple of chloroether sent for analysis lost hydrogen chloride conlpletel y when allowed t o stand, and analyzed as the dihydropyran. I-Iomever, the

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“…Thus, the 1,2,4,6-di-O-benzylidene derivatives of glucose (42) and (43; R = H or Bn) cleave rapidly with 1 equiv. Their behavior on reduction with H2AICI accords with the analysis outlined above; frequently only one product is obtained.…”

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Reduction of Acetals, Azaacetals and Thioacetals to Ethers

Brewster

1991

Comprehensive Organic Synthesis

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Steroids and Related Natural Products. VIII. Synthesis of Oxasteroids^1,2

Cited by 41 publications

References 2 publications

6H-Dibenzo[b,d]pyrans. I. Synthesis

6H-Dibenzo[b,d]pyrans. I. Synthesis

STEREOCHEMICAL STUDIES: VI. REACTIONS OF 3β-Hydroxy-4-Oxa-5α-Estrane AND 3α,17β-Dihydroxy-4-Oxa-5α-Estrane

Reduction of Acetals, Azaacetals and Thioacetals to Ethers

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Steroids and Related Natural Products. VIII. Synthesis of Oxasteroids1,2

Cited by 41 publications

References 2 publications

6H-Dibenzo[b,d]pyrans. I. Synthesis

6H-Dibenzo[b,d]pyrans. I. Synthesis

STEREOCHEMICAL STUDIES: VI. REACTIONS OF 3β-Hydroxy-4-Oxa-5α-Estrane AND 3α,17β-Dihydroxy-4-Oxa-5α-Estrane

Reduction of Acetals, Azaacetals and Thioacetals to Ethers

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Steroids and Related Natural Products. VIII. Synthesis of Oxasteroids^1,2