S. Padma

Synthetic studies towards prismanes: Seco-[6]-prismane

The first synthesis of seco-[6]-prismane 5, the closest, one-bond-away secologue of [6]-prismane 4, from the readily available Diels-Alder adduct of 1,5-cyclooctadiene and dimethoxytetrachlorocyclopentadiene is described. The key chemical operations in the 17 step sequence are (i) 4+2-cycloaddition of singlet oxygen 20 → 22, (ii) boron mediated fragmentation 47 → 14 and (iii) intramolecular 2+2-photocycloaddition 14 → 49. The methodology outlined here offers opportunities for further elaboration to [6]-prismane as well as several of its homo- and secologues.

Strain energy considerations in the photochemical [π2 + π2] cage cyclisations. A case study en route to [6]-prismane

Abstract Six novel cases of (2+2) photocycloaddition of strained cage dienes, aiming at producing [6]-prismane and congeners, are reported and the steric criteria for the success of reaction are presented based on molecular mechanics.

Synthetic studies towards prismanes: 1,4-Bishomo-[6]-prismane (“garudane”)

The first synthesis of 1,4-bishomohexaprismane 6, the true, face-to-face, heptacyclic dimer of norbornadiene ia delineated. In the initial phase, the readily available norborneno-p-benzoquinone 13 was transformed into the bishomoseco[7]-prismane dione 11 in three steps involving stereoselective 4+2 cycloaddition, regio- and stereoselective Ti3+ reduction of the enedione moiety and intramolecular 2+2-photocycloaddition. The versatile dione 11 through Favorskii ring contraction technology and subsequent functional group interconversions delivered the target hydrocarbon 6. The new synthetic methodology outlined here opens up avenues for the synthesis of many novel polyhedranes, in particular [6]-, [7]- and [8]-prismanes.

Theoretical and experimental study of [2+2]-photoclosure approachtoward [7]-prismane analogs

Abstract All 39 possible intramolecular [2+2]-photocycloaddition pathways toward [7]-prismane and its homo, seco, homo-seco, bishomo and bishomo-seco analogs have been explored by MM2 calculations. Fourteen of these are predicted to offer reasonable chance of success. Experimental support for a few of these is provided.

Synthetic studies towards prismanes: Exploratory efforts en route to [7]-prismane homo- and secologues

Abstract Novel heptacyclic triones 8 and 9 have been synthesised. A series of probing experiments on the heptacyclic ketones 3, 8 and 9, in quest for [7]-prismane homo- and secologues are described. Synthesis of novel polyhedranes 23–25 through thermal 2+2-cycloreversion of 3, 8 and 17, respectively, has been achieved. Our results point to the need for devising de novo strategy for the creation of higher prismanic frameworks.

π-Facial stereoselectivities in Diels–Alder cycloadditions to a dissymmetric cyclohexa-1,3-diene moiety in a novel, caged polycyclic framework

Novel polycyclic 1,3-dienes 4 and 5 have been synthesised and shown to undergo Diels–Alder cycloadditions exclusively from the carbonyl face. Steric environment seems to be predominantly responsible for the observed stereochemistry.

Stereoselective Synthesis of cis- and trans-Bicyclo [6.3.0] undec-4-en-10-ones. Efficient Precursors of 4-Oxo-1,2-Cyclopentane Dipropanoic Acids

Abstract Short syntheses of title compounds from cheap, readily available cis, cis-1,5-cyclooctadiene are described.

1,4-Bishomo[6]prismane (garudane): molecular structure and strain analysis of reactions potentially leading to prismanes

The proposed structure of garudane (1), the face-to-face D2h dimer of norbornadiene, has been confirmed by the X-ray analysis of a single crystal of the 1,3-bis(methoxycarbonyl) derivative (2), monoclinic, space group C2/c, a= 16.570(6), b= 8.073(4), c= 12.151(4)A, β= 114.89(2)°, final R= 0.055, Rw= 0.070. Detailed structural characteristics observed for (2) are compared with the isomeric D2d dimer (isogarudane)(3). Compound (1) is calculated to be 44 kcal mol–1 mere strained than (3). The demethylenation procedure on (1)—and the 1,4-bis homo[7] prismane (10) of similar structure—as a potential synthetic route to [6]- and [7]-prismanes (4) and (5) has advantages over the intramolecular [2 + 2]-photocyclization of polycyclic dienes [e.g.(12) and (13)] and the pinacolic coupling of polycyclic diketones [e.g.(14)]. These are discussed on the basis of strain analysis.