Solvolysis of 1-pent-3-ynyl triflate. Mechanism of the homopropargyl rearrangement

Hanack, Michael; Collins, Clair J.; Stutz, H.; Benjamin, Ben M.

doi:10.1021/ja00399a036

Cited by 18 publications

(4 citation statements)

References 4 publications

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“…The homopropargyl bromide was completely unreactive toward this dianion. Iodide 8a, while unreactive at -78 °C, produced trace amounts of alkylation product 23 when the reaction mixture was allowed to warm to -20 °C for 2 h. When the more reactive 3-pentynyl triflate (22b) 24 was employed, alkylation occurred smoothly at -78 °C to deliver 23 in a 60% yield. Although the relative stereochemistry of this product was not determined, a single stereoisomer was formed and is presumed, on the basis of literature precedent, 23 to be as depicted in 23.…”

Section: Resultsmentioning

confidence: 99%

“…The organic layer was separated, washed with water (2 × 50 mL) and brine (2 × 50 mL), dried (MgSO 4 ), and concentrated to afford a red oil. Filtration through a short column of basic alumina (pentane) gave 9.90 g (91%) of the known triflate 22b as a somewhat unstable orange oil: 1 H NMR (CDCl 3 , 300 MHz) δ 4.52 (t, J = 6.8 Hz, 2H), 2.63−2.70 (m, 2H), 1.78 (t, J = 2.4 Hz, 3H); 13 C NMR (CDCl 3 , 75 MHz) δ 118.6 (q), 79.3, 74.5, 71.7, 22.3, 3.3; IR (film) 1208, 947 cm -1 ; MS (EI) m / e 216.0075 (216.0068 calcd for C 6 H 7 F 3 O 3 S, M), 133, 105, 99, 66. Anal.…”

Section: Experimental Sectionmentioning

confidence: 99%

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Halide-Terminated N-Acyliminium Ion−Alkyne Cyclizations: A New Construction of Carbacephem Antibiotics

et al. 1997

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A series of 4-(3-alkynyl)azetidinones 13 was prepared from 4-(phenylsulfonyl)azetidine-2-one (9) and isopropyl glyoxylate hydrate. The 3-pentynyl (13a) and 4-phenyl-3-butynyl (13b) azetidinone acetates underwent 6-exo cyclization when treated with 3 equiv of SnCl4 at 0 °C to provide 3-(1-chloroalkylidene)carbacephems 15a (65%) and 15b (33%) respectively. In contrast, the 3-butynyl (13d) and 4-(trimethylsilyl)-3-butynyl (13c) azetidinone acetates underwent 7-endo cyclization under similar conditions to give 1-azabicyclo[5.2.0]nonenes 14a (11%) and 14b (71%), respectively. Beginning with penicillin degradation product 18, the more elaborate 3-pentynyl azetidinone cyclization substrate 27 was prepared in seven steps. Exposure to 27 to 3 equiv of SnCl4 in CH2Cl2 at 0 °C for 6 h, followed by allowing the reaction mixture to warm to rt, provided the desired 3-(1-chloroethylidene)carbacephem 28 in 60% yield and high (>99%) enantiometric purity. Cleavage of the chloroethylidene group of 28 with ozone gave 3-hydroxy carbacephem 29 in 77% yield. Since this intermediate has been converted in three steps to loracarbef (3), a new formal total synthesis of this carbacephem antiboitic was concluded.

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Section: Resultsmentioning

confidence: 99%

Section: Experimental Sectionmentioning

confidence: 99%

Halide-Terminated N-Acyliminium Ion−Alkyne Cyclizations: A New Construction of Carbacephem Antibiotics

et al. 1997

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“…Homopropargyl derivatives of type 432 are mostly converted into cyclobutanones 433. 210 The mechanism of the homopropargyl rearrangement has been determined based on the investigation of the solvolysis of functionally substituted alkylidenecyclopropanes 22 and cyclobutenes 211 as well as various open-chain and cyclic propargyl derivatives. 212,213 Studies of isotope effects involved in the solvolysis 121 and stereochemical aspects of the rearrangements of chiral pentynyl triflates 214 have also been invoked.…”

Section: Alkynyl Carbocations With a Remote Triple Bondmentioning

confidence: 99%

“…The results of these studies led to the conclusion that the solvolysis directly proceeds to the cations 428 and 429 via a transition state typical of S N 2 type reactions. 27,121,210 However, it has been shown for the solvolysis of cyclobut-1-enyl nonaflates 434 in trifluoroethanol that the presence of substituents stabilising the cationic centre at the 3-position of the ring is favourable for the formation of…”

Section: Alkynyl Carbocations With a Remote Triple Bondmentioning

confidence: 99%