A new estimate of the surface composition of exposed parts of the Canadian Precambrian Shield has been obtained, using samples of 122 rocks from northern Quebec–Ungava, 116 from Baffin Island, 116 from southwestern Quebec, 64 from northeastern Alberta, 18 from northern Saskatchewan, and 8076 from northern Ontario. Where feasible an interpenetrating replicate sampling design was used, with probability weighting by rock-type, analyzing both individuals and composites for trace elements, but only composites for major elements, A total of 385 triplicate spectrographic analyses and 48 major-element analyses were made.Regional differences between the six samples were detected; whether these also include secular variations could not be studied. The overall estimate follows:[Formula: see text]The major elements are similar to those found in granditorite, mica paragneiss, or graywacke, but the trace elements agree better with the last two only. Data for Th and U will follow later.The Precambrian Shield of Canada (and Fennoscandia also) contains more Si and K, and less Ti, Fe, Mn, Mg, and Ca than recent estimates of the whole crust of the earth.
Treatment of the acetylene-substituted cyclobutanone oxime ether (13) with (Me3Si)3SiH leads, in one pot, to the 5,6-bicyclic enone oxime (14) in 70% yield. It is suggested that the formation of (14) from (13) proceeds by way of a novel double ring expansion-transannulation process involving aminyl radical intermediates (see Scheme 3, below). By contrast, treatment of the cyclobutanone (3a) with Bu3SnH instead leads only to the product (11) of hydrostannylation of the acetylene unit in (3a). Neither (3a) nor (13) produced any of the expected bicyclo[3.3.0]octane products, viz. (5a) and (15), following treatment with silanes or stannanes. When a solution of the vinyl bromide-substituted cyclobutanone oxime (42) was irradiated with a sunlamp in the presence of (Me3Si)3SiH, the main product isolated was the triquinane (45) (38%) resulting from a cascade radical 6-exo-trig cyclization, aminyl radical fragmentation, 5-exo-trig radical transannulation, 5-exo-trig cyclization sequence.
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