“…Hence, the key feature to utilize these anions for successful intramolecular annulation relies heavily on their kinetic differentiations toward these two functionalities. The prerequisite is that the anion should react more rapidly with the propargyl halides . We first examined the cyclization of the substrates 1a , b with these metal anions; Scheme summarizes the results.…”
Section: Resultsmentioning
confidence: 99%
“…No effective method is yet available to cyclize these substrates chemoselectively. Selective syntheses of these alcohols can be accomplished by the intramolecular coupling of allenyl- or alkynylsilane with tethered ketones and aldehydes , even though the synthesis of these silyl substrates requires extra work. 1 …”
Metal carbonyl salts CpW(CO) 3 Na, Re(CO) 5 Na, and CpFe(CO) 2 Na were used for intramolecular cyclization of 1-(3-bromo-1-propynyl)-2-(3-oxopropyl)benzene. Among these salts, CpW(CO) 3 Na was found to be the most effective in yielding a metalated fused η 1 -2,5-dihydro-3-furyl complex. To generalize this cyclization, a number of organic substrates containing propargyl bromide and tethered aldehyde or ketone were prepared. Cyclizations of these substrates by CpW(CO) 3 Na proceeded with moderate yields (50%-65%), producing fused tungsten-η 1 -2,5-dihydrofur-3-yl compounds of five-, six-, and seven-membered rings. Demetalations of these organometallic products by (NH 4 ) 2 Ce(NO 3 ) 6 in CH 3 OH/CH 2 Cl 2 under flowing CO provided fused 3-(methoxycarbonyl)-2,5dihydrofurans; the yields were 50-60% for most cases. Consecutive oxidations of the representative η 1 -2,5-dihydrofur-3-yl complex 15 to its fused η 1 -2-furyl and further to η 1 -butenolide derivative were accomplished in good yields. Demetalations of these two fused η 1 -heterocycles were successful for η 1 -butenolide but not for the η 1 -2-furyl derivative.
“…Hence, the key feature to utilize these anions for successful intramolecular annulation relies heavily on their kinetic differentiations toward these two functionalities. The prerequisite is that the anion should react more rapidly with the propargyl halides . We first examined the cyclization of the substrates 1a , b with these metal anions; Scheme summarizes the results.…”
Section: Resultsmentioning
confidence: 99%
“…No effective method is yet available to cyclize these substrates chemoselectively. Selective syntheses of these alcohols can be accomplished by the intramolecular coupling of allenyl- or alkynylsilane with tethered ketones and aldehydes , even though the synthesis of these silyl substrates requires extra work. 1 …”
Metal carbonyl salts CpW(CO) 3 Na, Re(CO) 5 Na, and CpFe(CO) 2 Na were used for intramolecular cyclization of 1-(3-bromo-1-propynyl)-2-(3-oxopropyl)benzene. Among these salts, CpW(CO) 3 Na was found to be the most effective in yielding a metalated fused η 1 -2,5-dihydro-3-furyl complex. To generalize this cyclization, a number of organic substrates containing propargyl bromide and tethered aldehyde or ketone were prepared. Cyclizations of these substrates by CpW(CO) 3 Na proceeded with moderate yields (50%-65%), producing fused tungsten-η 1 -2,5-dihydrofur-3-yl compounds of five-, six-, and seven-membered rings. Demetalations of these organometallic products by (NH 4 ) 2 Ce(NO 3 ) 6 in CH 3 OH/CH 2 Cl 2 under flowing CO provided fused 3-(methoxycarbonyl)-2,5dihydrofurans; the yields were 50-60% for most cases. Consecutive oxidations of the representative η 1 -2,5-dihydrofur-3-yl complex 15 to its fused η 1 -2-furyl and further to η 1 -butenolide derivative were accomplished in good yields. Demetalations of these two fused η 1 -heterocycles were successful for η 1 -butenolide but not for the η 1 -2-furyl derivative.
“…Selective deprotection of the primary alcohol 12 by treatment with tetrabutylammonium fluoride [11] and subsequent oxidation [9] of the alcohol 13 yielded the aldehyde 14. The ring closure [12] of 14 to 15 could be achieved in 77% yield by transformation of the alkyne unit to the corresponding anion with lithium bis(trimethylsilyl)amide. [13] The ring closure generates a third stereogenic center in 15.…”
The fourteen‐membered ring of 7,7,12,12‐tetramethyl‐1,4‐dioxacyclotetradecane‐8,9,10,11‐tetrone (4) was built up from 1,2‐bis(2′‐chloroethoxy)ethane, two units derived from isobutyric acid and acetylene. Key intermediates were 2,2,11,11‐tetramethyl‐5,8‐dioxadodecane‐1,12‐diol (8), 7,7,12,12‐tetramethyl‐1,4‐dioxa‐9‐cyclotetradecyne‐2,8‐diolprotected by one tetrahydropyran group (15), and 8,11‐dihydroxy‐7,7,12,12‐tetramethyl‐1,4‐dioxacyclotetradecane‐9,10‐dione (18). X‐ray investigation on single crystals of the (R,S) isomer 18a revealed a transannular interaction between the dioxaethane bridge and the dicarbonyl moiety. Calculations (HF/6‐31G*) on 4 predict relatively short distances between the oxygen atoms of the dioxyethane bridge and the (CO)4 part. Investigations by means of cyclic voltammetry, PE and UV/Vis spectroscopy on 4 reveal an interaction between the dioxaethane bridge and the (CO)4 group.
“…An alternate route to the critical large ring was via a ring-forming acetylide addition to an aldehyde (Scheme 3) . The Wulff reaction 18 converted triflate 14 to the corresponding trimethylstannane ( 18 ), a compound that was prone to proto-destannylation during chromatographic purification.…”
[reaction--see text] The core structure of phomactins C and D was assembled by an efficient strategy starting from 3,4-dimethylcyclohexen-2-one. Key reactions include (1) a high yielding and highly diastereoselective Michael addition of a mixed cuprate, (2) a carbonylative alkyne-enoltriflate coupling or an intramolecular addition of an acetylide onto an aldehyde to form the macrocycle, (3) chemoselective Michael addition of a cuprate to an enynone, to give the carbon framework of desformyl phomactin C or D, and finally (4) regioselective addition of a thia-nucleophile to the more reactive beta-position of the resulting dienone.
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