Acid-catalyzed rearrangements of cyclobutanones

Erman, William F.; Treptow, Richard S.; Bakuzis, Peter; Wenkert, Ernest

doi:10.1021/ja00732a018

Cited by 41 publications

(9 citation statements)

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“…The optical rotations we have recorded using enantiomerically pure samples of compounds 3a , 3b , and 49b (filifolone) give the true dimension of the rotational strengths of these compounds. The magnitudes of the rotational strengths of these optically pure bicyclo[3.2.0]hept-3-en-6-ones are consistent with the geometric structures of this type of unsaturated ketone chromophore, in which the overlap of the olefinic π and π* orbitals create an intense charge-transfer band and the overlap of non bonded p and olefinic π orbitals causes the coupling of the transitions 3 Optical properties and absolute configurations of some bicyclo[3.2.0]hept-3-en-endo-6-ols and bicyclo[3.2.0]hept-2-en-6-ones …”

Section: The Bicyclo[320]hept-3-en-6-one Approach: a Unified Synthet...supporting

confidence: 56%

The Bicyclo[3.2.0]heptan-endo-2-ol and Bicyclo[3.2.0]hept-3-en-6-one Approaches in the Synthesis of Grandisol: The Evolution of an Idea and Efforts to Improve Versatility and Practicality

Marotta

Righi

Rosini

1999

Org. Process Res. Dev.

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In this paper we will disclose a chemistry story that started with a single molecule, the monoterpene grandisol, used in protecting cotton crops from an important pest, Anthonomus grandis Boheman. Initially, efforts were aimed at giving ever more practicality, versatility, and efficiency to a synthetic scheme that was centered on the key role of the 2,5-dimethylbicyclo[3.2.0]heptan-endo-2-ol, available from intermolecular photocyclization and methylation or, better and more conveniently, by an intramolecular copper(I)-catalyzed photobicyclization of the 3,6-dimethylhepta-1,6-dien-3-ol. We have developed an enantiospecific synthesis of both enantiomers of grandisol although some drawbacks would preclude scale up and commercialisation. The major limits of this original single-target synthetic scheme are pointed out along with the changed landscape resulting from recent developments in the fields of bioorganic chemistry and entomology. These changes prompted the elaboration of a new strategy focused on the conception and the development of a practical and efficient preparation bicyclo[3.2.0]hept-2-en-6-ones. The “bicyclo[3.2.0]hept-2-en-6-one approach” stems from a very convenient and general preparation, without photochemical steps, of bicyclo[3.2.0]hept-2-en-6-ones. These compounds proved to be amenable to selective manipulations to prepare not only grandisol but also other important molecules such as lineatin, filifolone, and raikovenal in multitarget and versatile synthetic schemes. Moreover, through resolution of the bicyclo[3.2.0]hept-2-en-6-ones, the procedures can be used to produce enantiomerically pure products. The bismethylation of the carbon atom adiacent to the carbonyl group as well as the conversion into the corresponding unsaturated bicyclic lactones are two important reactions that amplify the potential utility of bicyclo[3.2.0]hept-2-en-6-ones. Their peculiar reactivity, ascribed to the fact that the carbonyl group and the carbon−carbon double bond are attached to the same bridge-head carbon atom, has been demonstrated by the high chemio-, regio-, and stereoselectivity of the NBS-induced lactonization.

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Section: The Bicyclo[320]hept-3-en-6-one Approach: a Unified Synthet...supporting

confidence: 56%

The Bicyclo[3.2.0]heptan-endo-2-ol and Bicyclo[3.2.0]hept-3-en-6-one Approaches in the Synthesis of Grandisol: The Evolution of an Idea and Efforts to Improve Versatility and Practicality

Marotta

Righi

Rosini

1999

Org. Process Res. Dev.

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“…Ketone 33 always was accompanied by an extraneous ketone 39,35 which could be shown to originate by rearrangement of 33, but not of 34, on the gpc column or at the gpc injection port (165°). 22 l-Methyl-7-oxabicyc!o[4.2.0]octane (35b). A solution of 68 mg of sodium borohydride in 5 ml of ethanol was added dropwise to a solution of 1.00 g of tosylate 31a in 10 ml of ethanol at 0°and the mixture was stirred at room temperature for 15 hr.…”

Section: Methodsmentioning

confidence: 99%

Homo-Favorskii rearrangement

Wenkert¹,

Bakuzis²,

Baumgarten³

et al. 1971

J. Am. Chem. Soc.

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of 5 by benzophenone and acetone is attributed to eq 13, energy transfer to B to regenerate A. Since eq 13 simply increases the steady-state concentration of A and eq 8 and 12 have been included, operation of eq 13 can enhance the yield of 4 as well as that of 5.The observed results can be explained by assuming that A and B are tetramethylcyclobutadienes differing in multiplicity, one a singlet state and the other a triplet. Conversion of A to B, eq 10, could easily be assisted by long-lived radical species (02,-CCE, and other intermediates) or by heavy atoms in the solute. This could also explain the sensitivity of Gs to impurities present in the additives and those building up during the course of the irradiation. It is tempting to suggest that A is a triplet cyclobutadiene and B is a lower energy singlet. Theoretical calculations52 suggest that for free cyclobutadiene a "rectangular" singlet should lie 14-21 kcal/mol below a "square" triplet.Recent experimental evidence appears to indicate a rectangular singlet is the ground state of cyclobutadiene.53 Such an energy difference would explain a lack of quenching of A (and hence 5) by azulene ( « 31-39 kcal/mol)54 and other additives with higher triplet energies. Presumably lack of observed increases in G5 could be due to short lifetimes for triplets (52) M.

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“…42 More recently, this reaction was extended to both (6E)-and (6Z)-farnesic acid (39b and 39c), which stereospecifically gave 43b and 43c, respectively.43 Erman et al have studied, the mechanism of this reaction. 58 They proposed that 39a is converted to the mixed anhydride 40a, which loses acetic acid to give 41a, which cyclizes to give chrysanthenone (42a). Under the reaction conditions chrysanthenone is not stable but rearranges to filifolone (43a) by a series of Wagner-Meerwein shifts initiated by protonation of the carbonyl group.…”

Section: B Ketoketenesmentioning

confidence: 99%

Intramolecular cycloaddition reactions of ketenes and keteniminium salts with alkenes

Snider¹

1988

Chem. Rev.

209

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Contents I. Introduction 793 A. Ketene Generation 793 B. Tether Length 794 C. Effect of Substituents on the Alkene 794 D. Reaction Conditions 794 II, Substituents on the Ketene 794 A. Aldoketenes 795 1. Thermal Cycloadditions 795 2. Photochemical Addition of Aldoketenes 795 to the Double Bonds of u./S-Unsaturated Carbonyl Compounds B. Ketoketenes 796 C. a,/i-Unsaturated Ketenes 796 1. Type III Cycloadditions of 797 «,/3-Unsaturated Ketenes 2. Type II Cycloadditions of 799 a,d-Unsaturated Ketenes 3. Type I Cycloadditions of 801 a\ij-Unsaturated Ketenes D. Cyclopropylketenes 802 E. Arylketenes 802 F. Chloroketenes 803 G. Alkoxyketenes 803 FI. cr-Ketoketenes 804 I. Sulfonylketenes 805 J. Iminoketenes 805 K. Miscellaneous Ketenes 805 L. Cycloaddition of Ketenes to Carbonyl 806 Compounds III. Keteniminium Salts 806 A. Aldoand Ketoketiniminium Salts 806 B. Alkoxyketeniminium Salts 807 IV. Cycloreversion of Polycyclic Cyclobutanones 808 V. Conclusion 808 VI. Addendum 808 VII. References and Notes 810

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Acid-catalyzed rearrangements of cyclobutanones

Cited by 41 publications

References 4 publications

The Bicyclo[3.2.0]heptan-endo-2-ol and Bicyclo[3.2.0]hept-3-en-6-one Approaches in the Synthesis of Grandisol: The Evolution of an Idea and Efforts to Improve Versatility and Practicality

The Bicyclo[3.2.0]heptan-endo-2-ol and Bicyclo[3.2.0]hept-3-en-6-one Approaches in the Synthesis of Grandisol: The Evolution of an Idea and Efforts to Improve Versatility and Practicality

Homo-Favorskii rearrangement

Intramolecular cycloaddition reactions of ketenes and keteniminium salts with alkenes

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