Triangulanes branched

The synthetic procedure described by Arora and Binger [lb] to prepare 461 was extensively applied to the synthesis of unbranched 634 [172,6e] and branched 633, and 635—636 [173,172b] triangulanes. The sequence is based on the addition of a chloromethyl carbene to an appropriate methylenecyclo-... 

New procedures, in addition to the previous one, were developed to obtain higher branched triangulanes [174]. 

The addition of different types of carbenes onto bicyclopropylidene (1) is a common method for the preparation of [3]triangulane derivatives as well as branched trianguianes and normally proceeds without complications (for a review see [77]). Thus, the cyclopropanation under Gaspar-Roth [60] or modified Simmons-Smith [111] conditions gave dispiro[2.0.2.1]heptane ([3]triangulane, 97) in 80 [105] and 15% yield [5], respectively (Scheme 23). The palladium(II) acetate-catalyzed cycloprop anation of 1 with diazomethane, however, gave a number of products resulting from insertion of one or more than one methylene units into an initially formed palladacyclobutane 115 [112,113] (Scheme 23). 

The addition of methylchlorocarbene onto bicyclopropylidene (1) (Scheme 26) and functionalized bicyclopropylidenes like 44a and 121 has been used as a key step in the synthesis of branched triangulanes [53,122-1241. This was applied... 

Scheme 26. Application of methylchlorocarbene addition onto 1 for the preparation of branched [n]triangulanes [65,122,123]...

Scheme 27. Preparation of branched triangulanes 128,129 via carbene cycloadditions [33,65,105]...

For classification purposes, triangulanes have been divided into three types—linear (43), branched (4) and cyclic (44)9. Compounds 45 and 46 can be considered as precursors to unknown, extremely strained [4]- and [5]cyclotriangulanesM 65. 

The second method for the chain branching is based on the preparation of the alternative triangulane derivative 54, which also possesses a methylenecyclopropyl fragment and a tetrahydropyranyloxymethyl substituent73. This kind of precursor was prepared by cycloaddition of chloro(tetrahydropyranyloxyethyl)carbene to a methylenetriangulane followed by dehydrochlorination (equation 40). 

Both procedures were successfully used for the preparation of branched triangulanes 50 and 51 as well as for the previously unavailable [6]triangulane 5570,73 75. 

The preparation of other branched triangulanes with varying symmetries has also been reported. A notable feature of this series of small hydrocarbon cascades is that the framework is composed entirely of quaternary, tetraalkyl-substituted carbons. This unique architecture closely resembles or is at least reminiscent of Maciejewski s 16 proposed cascade molecule comprised of an all 1 — 3 C-branched interior framework (i.e., without spacers between branching centers). 

Scheme 4.17. Synthesis of branched triangulane possessing adjacent, quaternary carbon moieties. R = Me or THR...

In addition to linear and branched triangulanes, a new class of triangulanes, cyclic triangulanes 3 (CT), has been proposed as an additional subclass of triangulanes. ... 

A sequence of carbene additions to methylenetriangulanes can be used to build branched triangulanes. i - 3 3 When chloro(methyl)carbene generated from 1,1 -dichloroethane with butyl-lithium is used, new exocyclic double bonds for further cyclopropanation reactions can be generated by HCl elimination. For the same purpose l,l-dichloro-3-methoxypropane... 

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