Unsaturated neopentyl compounds. The effect of methyl substitution on the solvolytic course of homoallenic brosylates

Abstract

The acetolysis products of a series of 2,2-dimethyl-3,4-pentadienyl p-bromobenzenesulfonates with methyl substituents at C-3 and/or C-5 have been determined at 40 or 55°. In the absence of a methyl substituent at C-3, the starting brosylates yield rearranged allenic products exclusively: 2-methyl-4,5-hexadien-2-yl acetate, 2-methyl-2,4,5-hexatriene, and/or 2-methyl-1,4,5-hexatriene with one or two methyl substituents at C-5. When the starting brosylate has a methyl substituent at C-3, the acetolysis also yields cyclobutane-ring-containing acetates and hydrocarbons, as well as conjugated and/or cross-conjugated rearranged acyclic nonallenic trienes. The effect

Tin-Mediated Free-Radical Cyclization of β-Allenylbenzoyloximes

“…To our knowledge, only one case of 6-endo ring closure of a C-explained by stereoelectronic or steric effects as is the case ( shown, [17] that cannot be explained by π delocalization of a 2  solution of oxalyl chloride in CH 2 Cl 2 was added to a solution of the β-allenyl acid (3.08 g, 20 mmol) [10] in 5 mL of anhydrous CH 2 Cl 2 at 0°C. The reaction mixture was stirred at 20°C for 1 h, Conclusion and excess oxalyl chloride was then removed under reduced pressure.…”

“…The aqueous phase was extracted with General: Melting points are uncorrected. [10] and then by oxidation of the resulting β-al-20.5 (CH 3 ), 25.3 (CH 3 ), 38.6 [C(CH 3 ) 2 ], 95.6 (CϭCϭCH), 97.0 lenyl alcohols by PCC. [11] The crude ketones were purified by silica- 2,2,5-Trimethyl-1-phenylhexa-3,4- …”

“…The β-allenylaldehydes 2 can easily be obtained from the alcohols 1. [10] Grignard reagent addition to 2, followed by PCC oxidation [11] of the crude alcohols affords the ketones 3. Cannizzaro reaction with 2b (R 1 ϭ R 2 ϭ CH 3 ) gives the corresponding β-allenyl acid [10] which is converted into the acid chloride.…”

“…[10] Grignard reagent addition to 2, followed by PCC oxidation [11] of the crude alcohols affords the ketones 3. Cannizzaro reaction with 2b (R 1 ϭ R 2 ϭ CH 3 ) gives the corresponding β-allenyl acid [10] which is converted into the acid chloride. Compound 4 is then obtained by Arbusov reaction [12] of this acid chloride with triethyl phosphite.…”

1,5‐electrocyclization versus 1,5‐proton shift in imidazolium allylides and 2‐phospha‐allylides: a DFT investigation

“…3‐Imidazolium allylides ( 7 ) and 2‐phosphaallylides ( 8 ), besides undergoing intramolecular 1,5‐electrocyclization (Path A, Scheme 3), present another possibility, namely 1,5‐proton shift. Intramolecular 1,5‐proton shift has been observed frequently23–29 and it has been found to occur under mild conditions. In accordance with the reported basic character of the N ‐heterocyclic ylides,30 and phosphonium and arsonium ylides,23 and detection of a strong 1,5‐electrostatic interaction between the C2H proton of the pyridine ring and the negatively charged oxygen of the carbonyl function in the pyridinium phenacylides,30 it might be expected that C2H of the imidazolium allylides and 2‐phosphaallylides would undergo intramolecular 1,5‐shift leading to the generation of an imidazol‐2‐ylidene carbene ( 11 ) and its 2‐phospha analogue ( 12 ), respectively (Path B, Scheme 3).…”