0-Iodo acetals, synthesis

From Malonic Ester.—The same constitution is also proven by an interesting synthesis from malonic ester. Mono-sodium di-ethyl malonate reacts with monobrom, or mono-iodo acetic acid, and yields the ester of a tri-carboxy acid which after hydrolysis to the acid loses carbon di-oxide and yields succinic acid. 

A high degree of chiral transmission is observed in the synthesis of iodo acetal 19, a key intermediate in the total synthesis of ( + )-faranal (a trail pheromone of the Pharaoh s ant). The [2,3] Wittig process ot 16 followed by cis hydrogenation gives oxy-Cope substrate 17 with 100% E and Z and >99% threo. The oxy-Cope process of 17 affords en7//ro-aldehyde 18 as a single product with 91 % ee966. 

Kato and Hirata have described the synthesis of the desisopropyl sesquiterpene geijerene (237), starting from the iodo-acetate (236) [derived from (— )-santonin and previously used in the synthesis of shyobunone] as outlined in Scheme 23. 

A considerable simplification of the synthesis is owed to the work of Gunther HUlmann (1919-1975) and his wife Anneliese. [92] 3,5-Diiodotyrosine can be etherified directly with a 4,4 -dimethoxyphenyliodonium salt. [93, 94] After acidic cleavage of the protecting groups, iodmation occurs with N-iodo-acet amide. 

The Synthesis of 16, 17 -lmino-5a-androstan-3 -ol via 16 -Azido-17a.-iodo-5oL-androstan-3 -oi Acetate n4,137... 

Viprostol (81) also incorporates a hydroxy group moved to C-16 and protects this from facile metabolic oxidation by vinylation. It is a potent hypotensive and vasodilatory agent both orally and transdermally. The methyl ester moiety is rapidly hydrolyzed in skin and in the liver so it is essentially a prodrug. It is synthesized from protected E-iodo olefin 78 (compare with 75) by conversion to the mixed organocuprate and this added in a 1,4-sense to olefin 79 to produce protected intermediate 80. The synthesis of viprostol concludes by deblocking with acetic acid and then reesterification with diazomethane to give 81 [19]. 

This procedure for the synthesis of ethyl 3-nitroacrylate is essentially that of Stevens and Emmons.2 Four major changes have been introduced by the submitters rapid introduction of dinitrogen tetroxide no purification of the intermediate nitro iodo ester use of dry, finely powdered sodium acetate for elimination of hydroiodic acid and percolation of the final product through a mat of alumina. With these modifications, the preparation is reproducible and highly efficient (80-90% overall). 

B. Reactions.—(/) Halides. Whereas ylides are alkylated in the normal way on treatment with a-bromo- or a-iodo-esters, quite different reactions occur with a-fluoro- and a-chloro-acetates. When salt-free ylides were refluxed in benzene with ethyl fluoroacetate or trifluoroacetate normal Wittig olefin synthesis took place with the carbonyls of the ester groups to give vinyl ethers, e.g. (14). On the other hand, methyl chloroacetate with... 

Synthesis of the dihydrothiophene derivatives was described by Flynn et al. [70] (depicted in Scheme 23) and involved the conversion of 3-butynol 92 to benzyl 3-butynal sulfide 93. Sonogashira coupling of the sulfide 93 with acetic acid 5-iodo-2-methoxyphenyl ester 94, produced the intermediate 95. Treatment of compound 95 with iodine resulted in a rapid and... 

Crich and Rumthao reported a new synthesis of carbazomycin B using a benzeneselenol-catalyzed, stannane-mediated addition of an aryl radical to the functionalized iodocarbamate 835, followed by cyclization and dehydrogenative aromatization (622). The iodocarbamate 835 required for the key radical reaction was obtained from the nitrophenol 784 (609) (see Scheme 5.85). lodination of 784, followed by acetylation, afforded 3,4-dimethyl-6-iodo-2-methoxy-5-nitrophenyl acetate 834. Reduction of 834 with iron and ferric chloride in acetic acid, followed by reaction with methyl chloroformate, led to the iodocarbamate 835. Reaction of 835 and diphenyl diselenide in refluxing benzene with tributyltin hydride and azobisisobutyronitrile (AIBN) gave the adduct 836 in 40% yield, along with 8% of the recovered substrate and 12% of the deiodinated carbamate 837. Treatment of 836 with phenylselenenyl bromide in dichloromethane afforded the phenylselenenyltetrahydrocarbazole 838. Oxidative... 

The first asymmetric synthesis of (-)-monomorine I, an enantiomer of the natural alkaloid, by Husson and co-workers starts with the chiral 2-cyano-6-oxazolopiperidine synthon (385) prepared from (-)-phenylglycinol (384), glu-taraldehyde (383), and KCN (443). Alkylation of 385 with an iodo ketal led to the formation of a single product (386). The cyano acetal (386) was treated with silver tetrafluoroborate and then zinc borohydride to afford a 3 2 mixture of C-6 epimeric oxazolidine (387) having the (2S) configuration. Reaction of 387 with... 

The Synthesis of 16fi,17fi-imino-5a.-androstan-3fi-o/ via 16fi-Azido-17[Pg.264]

W. R. Roush and C. E. Bennett, A highly stereoselective synthesis of 2-deoxy-P-glycosides using 2-deoxy-2-iodo-glucopyranosyl acetate donors, /. Am. Chem. Soc., 121 (1999)3541-3542. 

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